Unit 9 Genetics Biology 10 Unit 9 Genetics

Unit 9: Genetics Biology 10

Unit 9: Genetics Table of Contents • Lesson 9. 1: Genes and Alleles • Lesson 9. 2: Dominant vs. Recessive Alleles • Lesson 9. 3: Punnett Squares • Lesson 9. 4: Sex-Linked Traits • Lesson 9. 5: Pedigrees

Lesson 9. 1: Genes & Alleles Learning Objectives • I can define what a gene is, and explain that there can be more than one allele for each gene. • I can explain the difference between genotype and phenotype.

Genetics © Amy Brown Science

Genetics is… …. the science that studies how genes are transmitted from one generation to the next.

Genetics The study of heredity, how traits are passed from parent to offspring x or = or

Genes & Traits • Genes = carries information that determines your traits. • Traits are the characteristics that you inherit from your parents • Genes are sections of DNA located on chromosomes Chromosome: A long chain of genes.

Alleles • Alleles = different versions of the same gene (ex: blue eyes & brown eyes) • Organisms have two genes (alleles) for each trait. • One gene (allele) from mother (egg). • One gene (allele) from father (sperm). • Alleles can be dominant or recessive

Lesson 9. 1: Genes & Alleles Learning Objectives • I can define what a gene is, and explain that there can be more than one allele for each gene. • I can explain the difference between genotype and phenotype.

Genotype vs. Phenotype • Phenotype = an organism’s physical traits. • the physical appearance of a trait in an organism • what you see; visible traits • Determined by looking at organism • Example: tall, short, brown eyes

Genotype vs. Phenotype • Genotype = an organisms genetic makeup • the genes of an organism for one specific trait • what’s in your DNA • Example: Tt, TT, tt

Unit 9: Genetics Table of Contents • Lesson 9. 1: Genes and Alleles • Lesson 9. 2: Dominant vs. Recessive Alleles • Lesson 9. 3: Punnett Squares • Lesson 9. 4: Sex-Linked Traits • Lesson 9. 5: Pedigrees

Lesson 9. 2: Dominant vs. Recessive Alleles Learning Objectives • I can explain the difference between dominant and recessive alleles. • I can determine the phenotype of an organisms based on a heterozygous or homozygous genotype.

Dominant gene (allele) • Stronger of two alleles for a gene • prevents the other allele from “showing” • Represented with capital letters • Written first • Example: B for black fur

Recessive gene (allele) • Weaker of two alleles for a gene • Can be hidden by dominant genes. • does NOT “show” if a dominant allele is also present • Represented with lower case letters • Example: b for white fur

Example: Straight thumb is dominant to hitchhiker thumb T = straight thumb t = hitchhikers thumb (Always use the same letter for the same alleles— No S = straight, h = hitchhiker’s) Straight thumb = TT Straight thumb = Tt Hitchhikers thumb = tt * Must have 2 recessive alleles for a recessive trait to “show”

Lesson 9. 2: Dominant vs. Recessive Alleles Learning Objectives • I can explain the difference between dominant and recessive alleles. • I can determine the phenotype of an organisms based on a heterozygous or homozygous genotype.

Homozygous (Pure) • Organism has two of the same genes (alleles) for a trait • Example: • BB – homozygous dominant • bb – homozygous recessive

Heterozygous (Hybrid; Mixed) • Organism has two different alleles for a trait • Example: • Bb – heterozygous (one dominant, one recessive)

Genotype or Phenotype? • Tt • Round • Black • BB • Smooth • rr • Tall

Unit 9: Genetics Table of Contents • Lesson 9. 1: Genes and Alleles • Lesson 9. 2: Dominant vs. Recessive Alleles • Lesson 9. 3: Punnett Squares • Lesson 9. 4: Sex-Linked Traits • Lesson 9. 5: Pedigrees

Lesson 9. 3: Punnett Squares Learning Objective • I can create Punnett squares to predict the genotypes from a monohybrid cross.

Punnett Square and Probability • Used to predict the possible gene makeup of offspring – Punnett Square • Example: Black fur (B) is dominant to white fur (b) in mice 1. Cross a heterozygous male with a homozygous recessive female. Black fur (B) Heterozygous male White fur (b) Homozygous recessive female White fur (b)

Before we go further lets learn how to set up a Punnett Square… We begin by constructing a grid of two perpendicular lines.

Next, put the genotype of one parent across the top and the other along the left side. For this example lets consider a genotype of BB crossed with bb. B b b B • Notice only one letter goes above each box • It does not matter which parent’s genotype goes on either side.

Next, fill in the boxes by copying the column and row head-letters down and across into the empty spaces. B B b Bb Bb

Punnett Squares • Now that we have learned the basics of genetics lets walk through some examples using Punnett Squares.

W w W WW Ww ww Usually write the capital letter first Lets say: W- dominant widow’s peak w- recessive no widow’s peak Parents in this cross are heterozygous (Ww). Note: Make sure I can tell your capital letters from lowercase letters. What percentage of the offspring will not have a widow’s peak? ANSWER: 25% (homozygous recessive)

Red hair (R) is dominant over blond hair (r). Make a cross between a heterozygous red head and a blond. R r r r Rr rr What percentage of the offspring will have red hair? 50%

Let’s try some more… In pea plants, tall pea plants (T) are dominant over short pea plants (t). Construct a Punnett Square for a heterozygous tall pea plant and a short pea plant. T t t Tt tt What are the percentage of phenotypes? 50% tall 50% short

Mouse Eye Color Black eyes (R) is dominant over red eyes (r) in rats. Make a cross between a homozygous rat with black eyes and a rat with red eyes. r R Rr r Rr Rr What is the possibility of a red eye off springs? 0%

Having dimples is dominant over the absence of dimples. Cross a heterozygous dimpled man with a woman who does not have dimples. Show all work in the Punnett square and summarize your findings in the table. What is the genotype of the man? Dd What is the genotype of the woman? D d Dd dd dd 2/4 Dd 2/4 dimples 2/4 no dimples

Normal skin is dominant over albino skin. A woman who has normal skin, but whose father was albino, marries a heterozygous, normal skinned man. What type of What ismight they genotype offspring expect? of the woman? Aa What is the genotype of the man? Aa A AA Aa aa 1/4 AA 2/4 Aa 1/4 aa ¾ Normal ¼ albino How many different genotypes are possible among the offspring? How many different phenotypes are possible among the offspring? What is the probability of getting homozygous offspring? What is the probability of getting heterozygous offspring? What is the probability of getting normal offspring? What is the probability of getting albino offspring? 3 2 2/4 3/4 1/4

In dogs, the allele for short hair (B) is dominant over the allele for long hair (b). Two short haired dogs have a litter of puppies. Some of the puppies have short hair and some of the puppies have long hair. What are the genotypes of the parents? Bb and Bb B BB Bb bb 1/4 BB 2/4 Bb 1/4 bb ¾ short hair ¼ long hair If the litter of puppies contained 12 pups, how many would you expect to have short hair? ¾ of the 12 should have short hair. ¾ of 12 = 9 pups How many would you expect to have long hair? ¼ of 12 = 3 pups

Practice Problems H 1. WHICH OF THE FOLLOWING HAS THE hh GENOTYPE? A. B. C. D. 1&3 2 4 NONE H 4 1 h 3 2 2. WHICH OF THE FOLLOWING IS A TRUE STATEMENT? A. B. C. D. h INDIVIDUAL 4 IS RECESSIVE INDIVIDUALS 1 & 3 ARE HETEROZYGOUS INDIVIDUAL 2 IS DOMINANT ALL INDIVIDUALS ARE FEMALE

Practice Problems 3. IF B IS THE ALLELE FOR BLACK FUR AND b IS THE ALLELE FOR WHITE FUR, WHAT PERCENT WOULD BE BLACK? A. B. C. D. 25% 50% 100% 75% B b B BB Bb bb 4. WHAT FRACTION IS HOMOZYGOUS DOMINANT IN THE ABOVE CROSS? A. B. C. D. 1/2 1/4 1/3 3/4

Practice Problems B 5. IN THIS CROSS, WHAT IS THE RATIO OF BB TO Bb? A. B. C. D. 3: 1 4: 1 2: 2 0: 4 B B BB BB b Bb Bb

In polygenic inheritance, the determination of a given characteristic is the result of: the interaction of many genes. size, height, shape, weight, color, metabolic rate, and behavior Some traits, such as _____________________ are not determined by one pair of alleles. These traits are the many genes This is cumulative result of the combined effects of ______. polygenic inheritance known as _________.

A trait affected by a number of genes or polygenes - does not show a clear difference between groups of individuals. Instead, it shows a: graduation of small differences Many normal human traits are thought to be polygenic. Examples: hair color eye color weight height skin color

Unit 9: Genetics Table of Contents • Lesson 9. 1: Genes and Alleles • Lesson 9. 2: Dominant vs. Recessive Alleles • Lesson 9. 3: Punnett Squares • Lesson 9. 4: Sex-Linked Traits • Lesson 9. 5: Pedigrees

Lesson 9. 4: Sex-Linked Traits Leaning Objectives • I can explain what a sex-linked trait is and describe the inheritance patterns for sex-linked traits using Punnett squares.

Sex Determination • Humans – 46 chromosomes or 23 pairs • 22 pairs are homologous (look alike) – called autosomes – determine body traits 1 pair is the sex chromosomes – determines sex (male or female) • Females – sex chromosomes are homologous (look alike) – label XX Males – sex chromosomes are different – label XY

• What is the probability of a couple having a boy? Or a girl? Chance of having female baby? 50% X X X XX XX Y XY XY Who determines the sex of the child? father

Sex – linked Traits • Genes for these traits are located only on the X chromosome (NOT on the Y chromosome) • X linked alleles always show up in males whether dominant or recessive because males have only one X chromosome

Sex-linked Traits • Males get only one allele for a sex-linked trait carried on the X chromosome (nothing on Y) • Females have a second X chromosome that carries another allele that can hide recessive trait • Therefore Males show recessive traits more than females

Sex-linked Traits Example: Colorblindness Sex Chromosomes Colorblindness gene XX chromosome - female copyright cmassengale XY chromosome - male 46

• Examples of recessive sex-linked disorders: 1. colorblindness – inability to distinguish between certain colors You should see 58 (upper left), 18 (upper right), E (lower left) and 17 (lower right). Color blindness is the inability to distinguish the differences between certain colors. The most common type is red-green color blindness, where red and green are seen as the same color.

2. hemophilia – blood won’t clot

Working Sex-linked problems The genotypes for colorblindness would be written as follows: XCXC = normal vision female XC Xc = normal vision female, but a carrier of the colorblind allele The genotypes for hemophilia would be written as follows: XHXH = normal blood clotting female XH Xh = normal clotting female, but a carrier of hemophilia Xc. Xc = Colorblind female Xh. Xh = hemophiliac female XCY = normal vision male Xc. Y = Colorblind male XHY = normal blood clotting male Xh. Y = Hemophiliac male

• Example: A female that has normal vision but is a carrier for colorblindness marries a male with normal vision. Give the expected phenotypes of their children. N = normal vision n = colorblindness XN Xn x XN Y XN Xn X NX N X NX n X NY X n. Y Y Phenotype: 2 normal vision females 1 normal vision male 1 colorblind male

The gene for colorblindness is carried on the X chromosome and is recessive. A man, whose father was colorblind, has a colorblind daughter. 1. Is this man colorblind? How do you know? Yes. The colorblind daughter had to get one of her genes for colorblindness from her father. 2. Where did the man get his gene for colorblindness? A man gets his gene for colorblindness from his mother. He gets his Y chromosome from his father. 3. Must the fathers of all colorblind girls be colorblind? Explain. Yes. For a girl to be colorblind, she must inherit the colorblind gene from each parent.

Practice Problem: A normal woman, whose father had hemophilia, married a normal man. What is the chance of hemophilia in their children? What is the genotype of the woman’s father? Xh. Y What is the genotype of the woman? XHXh What is the genotype of the man? XHY XH XH Y XHXh. Xh Xh Y 1/4 1/4 X H XH X H Xh X HY X h. Y 2/4 Normal female 1/4 Normal male 1/4 Hemophiliac male

Sex-linked Traits in Females • Females who have recessive alleles but show the dominant trait are called carriers • A woman can have normal vision but carry the recessive allele for colorblindness

Sex-linked Trait Problem • Example: Eye color in fruit flies • (red-eyed male) x (white-eyed female) XRY x X r • Remember: the Y chromosome in males does not carry traits. • RR = red eyed r r X X • Rr = red eyed • rr = white eyed • XY = male XR • XX = female Y copyright cmassengale 54

Sex-linked Trait Solution: Xr XR XR Xr Y Xr XR Xr Xr Y 50% red eyed female 50% white eyed male copyright cmassengale 55

Unit 9: Genetics Table of Contents • Lesson 9. 1: Genes and Alleles • Lesson 9. 2: Dominant vs. Recessive Alleles • Lesson 9. 3: Punnett Squares • Lesson 9. 4: Sex-Linked Traits • Lesson 9. 5: Pedigrees

Lesson 9. 5: Pedigrees Leaning Objective • I can draw pedigree charts illustrating the inheritance patterns of traits in a family.

Pedigrees • Graphic representation of how a trait is passed from parents to offspring • Tips for making a pedigree 1. Circles are for females 2. Squares are for males 3. Horizontal lines connecting a male and a female represent a marriage 4. Vertical line and brackets connect parent to offspring 5. A shaded circle or square indicates a person has the trait 6. A circle or square NOT shaded represents an individual who does NOT have the trait 7. Partial shade indicates a carrier – someone who is heterozygous for the trait

Male Parents Female Siblings Affected male Affected female Mating Known heterozygote s for recessive allele Death Pedigrees illustrate inheritance

• Example: Make a pedigree chart for the following couple. Dana is color blind; her husband Jeff is not. They have two boys and two girls. HINT: Colorblindness is a recessive sex-linked trait. X n Has trait X NY Can pass trait to offspring

A. A pedigree chart shows relationships within a family. B. Squares represent males and circles represent females. C. A shaded circle or square indicates that a person has the trait. D. The following table shows three generations of guinea pigs. In guinea pigs, rough coat (R) is dominant over smooth coat (r). Shaded individual have smooth coat. What is the genotype of each individual on the table below? rr Rr RR (probably) Rr Rr rr Rr / RR There is no way to know!

The following pedigree table is for colorblindness. This is a sexlinked trait. Shaded individual have colorblindness. Determine the genotype of each of the following family members. XC Xc Xc Y XC Y Xc Xc XCY XC Xc XC XC XC Xc

Pedigrees

Mutations • Mutation – sudden genetic change (change in base pair sequence of DNA) • Can be : Harmful mutations – organism less able to survive: genetic disorders, cancer, death Beneficial mutations – allows organism to better survive: provides genetic variation Neutral mutations – neither harmful nor helpful to organism • Mutations can occur in 2 ways: chromosomal mutation or gene/point mutation

Chromosomal mutation: • less common than a gene mutation • more drastic – affects entire chromosome, so affects many genes rather than just one • caused by failure of the homologous chromosomes to separate normally during meiosis • chromosome pairs no longer look the same – too few or too many genes, different shape

• Examples: Down’s syndrome – (Trisomy 21) 47 chromosomes, extra chromosome at pair #21

Turner’s syndrome – only 45 chromosomes, missing a sex chromosome (X) Girls affected – short, slow growth, heart problems

Klinefelter’s syndrome – 47 chromosomes, extra X chromosomes (XXY) Boys affected – low testosterone levels, underdeveloped muscles, sparse facial hair

• Having an extra set of chromosomes is fatal in animals, but in plants it makes them larger and hardier. Hardier

Detecting Genetic Disorders • picture of an individual’s chromosomes – karyotype • amniotic fluid surrounding the embryo is removed for analysis – amniocentesis Female with Down’s syndrome

TERMS TO KNOW ALLELES DIFFERENT FORMS OF A TRAIT THAT A GENE MAY HAVE HOMOZYGOUS AN ORGANISM WITH TWO ALLELES THAT ARE THE SAME TT, tt HETEROZYGOUS AN ORGANISM WITH TWO DIFFERENT ALLELES FOR A TRAIT Tt, Gg T, t

TERMS TO KNOW HYBRID SAME AS HETEROZYGOUS Tt, Gg DOMINANT A TRAIT THAT DOMINATES OR COVERS UP THE OTHER FORM OF THE TRAIT REPRESENTED BY AN UPPERCASE LETTER T G OR RECESSIVE THE TRAIT BEING DOMINATED OR COVERED UP BY THE DOMINATE TRAIT REPRESENTED BY A LOWER CASE LETTER t g or

TERMS TO KNOW PHENOTYPE THE PHYSICAL APPEARANCE OF AN ORGANISM (WHAT IT LOOKS LIKE) TALL, SHORT, GREEN, WRINKLED GENOTYPE THE GENE ORDER OF AN ORGANISM (WHAT ITS GENES LOOK LIKE) TT, GG, Tt, gg Gg, tt RATIO THE RELATIONSHIP IN NUMBERS BETWEEN TWO OR MORE THINGS 3: 1, 2: 2, 1: 2: 1