Unit 8 Meiosis and Mendel Genetics and Inheritance

Unit 8 Meiosis and Mendel Genetics and Inheritance Quiz Date: Jan. 11 /12 Test Date: Jan. 18/19

UNIT 8 - INTRODUCTION TO GENETICS • Although the resemblance between generations of organisms had been noted for thousands of years, it wasn’t until the 1800 s that scientific studies were carried out to develop an explanation for this. Today we know that we resemble our parents because of ________, which is the set of characteristics we receive from ___________. The study of heredity is known as _________. our parents genetics

I. SEXUAL REPRODUCTION & MEIOSIS (pp. 275 -278) • In sexual reproduction, an egg and sperm cell fuse together to create a fertilized egg or ________. zygote

A. Chromosome Number 1. Somatic Cells - _______ Body cells Human somatic cells contain ____ 46 chromosomes _______ or ____ meaning they contain a Diploid 2 n ______ set of chromosomes, half ( _____23) from double _____ Dad and half from ____. Mom “Matching” chromosomes are known as _____________________. Homologous pairs A homologous pair is made up of a copy of a chromosome from each parent, with the same ______. genes

Homologous Chromosomes

GAMETES 2. Gametes - ______ Egg and ________ Sperm cells Human gametes contain ______23 chromosomes. _______ or ______ meaning there is _____ Haploid n setone of instructions for each ______. gene When gametes fuse together in ___________, the zygote fertilization ________ diploid produced is _______ 46 and has _______ chromosomes.

Haploid vs. Diploid Karyotypes

B. Meiosis Special type of cell division that only occurs in specialized germ cells (sex cells) in ______ of femalesovaries and _______ oftestes males. In meiosis, DNA is replicated once but cell divides ________, resulting in ______ 2 X, two times 4 cells with _______ 1/2 the original chromosome number.

MEIOSIS In females, process is known as ____________. oogenesis In males, process is known as _____________. spermatogenesis In both males & females, prior to meiosis I, DNA is replicated during ______ of ____________. S interphase

Meiosis occurs in two stages:

1. Meiosis I Prophase I Unlike in prophase of mitosis, In prophase I______________ come together to form Homologous pairs a _______. tetrad Tetrads are held together at the __________. centromeres

Crossing Over Meiosis I Exchange of genetic information between a ________________ with its Sister chromatid __________________. Non-sister homologue Occurs very frequently Allows for _____________. Genetic variation

Meiosis I Metaphase I _______________ align in equator of Tetrads cell Each homologue consists of ____________________. Two sister chromatids Anaphase I _____________________ Homologous pairs _ are pulled apart _________, Centromeres Sister chromatids _____________ still intact

Meiosis I Telophase I Two cells are formed, each with _______ 23 chromosomes Each chromosome still composed of two __________ Sister chromatids Two cells produced at the end of meiosis I are ________ haploid There are no homologous pairs present because___________

MEIOSIS II

2. Meiosis II Continues with the two cells formed moving directly into prophase II without any further ___________ of DNA. Inreplication anaphase II, ___________ are pulled apart. Sister chromatids Two new cells are formed from each of the two cells formed in meiosis I, resulting in a total of ______ new cells, each with ______the original number of chromosomes. 4 Cells produced are called __________. 1/2 Gametes

3. Oogenesis vs. spermatogenesis • Spermatogenesis: Males produce 4 viable sperm cells • Begins: puberty ______ • Ends: death ______

3. Oogenesis vs. spermatogenesis • Oogenesis: Females produce only one egg and 3 polar bodies • Begins: ______ Before birth • Ends: ______ menopause

II. HISTORY OF GENETICS (pp. 263 -270) • A. Gregor Mendel Known as the “Father of ________” Genetics Famous for his experiments with ____ peaplants.

Mendel Used true-breeding pea plants, which means ____________; characteristics always pureline, purebred show. Known as the ______Pgeneration. Studied seven _______, including plant height, seed color, flower color, etc. traits o A trait is an ________________. Inherited characteristic

Mendel Pea plants cross-pollinate, meaning pollen from one plant fertilizes an egg from another, but they can also self-pollinate, meaning pollen can fertilize egg from _______ plant. Mendel controlled same the fertilization process of the pea plants by preventing _________________ and controlling Self-pollination __________________. Cross-pollination

Pea Traits Studied •

B. Mendel’s Results P generation – Crossed _________ True-breedingplants with one trait with ________ plants with the other. True-breeding For example, TT (tall) x tt (short) _______________________ F 1 generation – Offspring produced from _________. In F 1, one. P trait tall plants X short plants = X P______. For example, disappeared _____________. F 2 generation All tall– Offspring plantsproduced from _________. In F 2, trait that disappeared in F 1 reappeared in _____ of the. F 1 offspring; X F 1 the other ¾ showed _______________. 1/4 Dominant trait

Mendel’s Principles • C. Mendel’s Principles – After analyzing his results carefully, Mendel formed conclusions that increased understanding of inheritance and opened the door for the study of genetics. Individual units called ______ determine inheritable characteristics. A gene is a portion ofgenes ______ that codes for a specific ______. DNA trait

Alleles and Genes

Mendel’s Principles For each gene, an organism inherits two alleles, one from each _________. Alleles are different forms or parent __________ of a ______. For any given gene versions trait, homozygous its alleles are the same and the o If an organism is __________, trait will be expressed. o If the alleles differ, the organism is said to be __________ for thatheterozygous trait and only one allele will be expressed. The expressed allele is the _______ allele, designated by andominant _____-case letter. The allele that is not expressed in a heterozygous trait is upper _________, designated by a _______-case recessive letter. A recessive allele is only lower expressed when an organism is ________. homozygous

Mendel’s Principles Principle of Segregation - In meiosis, the two alleles for a trait segregate (________). separate Each egg or sperm cell receives a copy of one of the two alleles present in the somatic cells of the organism. There is a _____ chance that a copy of that allele will end up 50% in the gamete produced. Principle of Independent Assortment – The way one pair of alleles segregates has no influence on any other pair of alleles.

Independent Assortment

D. Genetics Terminology • 1. Phenotype - ________ description of trait; Physical for example, _______ Tall, short • 2. Genotype – Genetic make-up of an organism or set of alleles; for example, __________. TT, Tt, heterozygous, etc. .

Genetics Terminology • 3. Application of Terminology - If round pea seeds are dominant to wrinkled pea seeds, round is designated _____ and wrinkled is designated R ______. • a. r Homozygous dominant • Genotype = ____; Phenotype = ____ • b. Heterozygous RR round • Genotype = ____; Phenotype = ____ • c. Homozygous recessive round Rr • Genotype = ____; Phenotype = ____ rr wrinkled

III. ANALYZING INHERITANCE (pp. 135 -137) • A. Probability segregation Due to the law of________, if you know the genotype of the parents, you can predict the likelihood of a trait occurring in the offspring. Probability can be written 3 ways. The probability of a coin coming up heads after being flipped is (fraction) _____, 1/2 (ratio) ____, or (percent) _______. 50% 1: 2

B. Punnett Squares • A Punnett square is a tool used to predict the possible outcomes of ________ and meiosis __________; in other words, a Punnett fertilization square is used to determine the probability of certain traits appearing in offspring.

Punnett Practice Monohybrid crosses A-D • • Must have a key And Cross with Each problem For full credit

A: Construct a Punnett square to determine the probability of white flowers is a heterozygous purple flower (Pp) is crossed with a homozygous white flower (pp) P=purple, p=white 1. Key: ____________ 2. Cross: ________ Pp X pp p p Pp pp 50% Probability of White flowers: ______

B: Construct a Punnett square to determine the probability of short pea plants if a homozygous tall plant (TT) is crossed with a heterozygous tall plant (Tt) T=tall, t=short 1. Key: _________ 2. Cross: ________ TT X Tt T T 0% Probability of short pea plants: ______ T TT TT t Tt Tt 100% Probability of tall pea plants: ______

C: If round peas are dominant over wrinkled peas, make a Punnett square to determined the genotype and phenotype ratios of the offspring if a heterozygous plant is crossed with a homozygous recessive plant R=round, r=wrinkled 1. Key: _________ 2. Cross: ________ Rr X rr R r r Rr rr RR: Rr: rr 0: 2: 2 Genotypic ratio: _________ 2: 2 Phenotypic ratio: _________

D: Use a Punnett square to determine the genotype and phenotype ratios of the offspring from a cross between a homozygous dominant yellow pea plant and a homozygous recessive green pea plant Y=yellow, y=green 1. Key: _________ 2. Cross: ________ YY X yy Y Y y Yy Yy YY: Yy: yy 0: 4: 0 Genotypic ratio: ________ 4: 0 Phenotypic ratio: _________

Dihybrid crosses The punnett squares we have been doing are known as __________ crosses, monohybrid meaning that only one traits has been considered 2 at a time. In a dihybrid cross, _____ genes different _______ on 2 different _______ chromosomes are analyzed.

Punnett Practice dihybrid crosses A -B 1. Key 2. Cross 3. Punnet square

A. Peas homozygous for round shape and heterozygous for color are crossed with yellow peas heterozygous for shape Key: R=round, r=wrinkled Y=yellow, y=green Cross: ___________ Genotypic ratio: ___________________________ Phenotypic ratio: ______________

B. Key: G= gray body, g= black body; R=red eyes, r =black eyes Cross: GGRr X Ggrr What are the phenotypes of the parent fruit flies: ______________ Genotypic ratio: ______________ Phenotypic ratio: ______________

Incomplete Dominance • Neither allele has “complete” dominance over the other; heterozygous phenotype is a blend of the 2 homozygous phenotypes • Ex: snapdragons R = red W = white RW = pink

Incomplete Dominance: cross a pink snapdragon with a white snapdragon 1. Key: _____________ 2. Cross: ____________ Phenotypic ratio: __________ Genotypic ratio: __________

Incomplete Dominance: cross a red snapdragon with a white snapdragon 1. Key: _____________ 2. Cross: ____________ Phenotypic ratio: __________ Genotypic ratio: __________

Codominance • Codominance – Both alleles share dominance and are always expressed if present. • Ex: In chicken B = black feathers X W = white feathers BW = black AND white feathers

Codominance: cross a pink snapdragon with a white snapdragon 1. Key: _____________ 2. Cross: ____________ Phenotypic ratio: __________ Genotypic ratio: __________

Codominance: cross a pink snapdragon with a white snapdragon 1. Key: _____________ 2. Cross: ____________ Phenotypic ratio: __________ Genotypic ratio: __________

Polygenic Traits • “Many genes” ; Many traits are controlled by more than one gene; have a variety of choices for expression. • Ex: _hair color, eye color, skin tone

Multiple Alleles • Many genes that have more than 2 alleles, although an individual only has 2 alleles for the gene. • Ex: blood group. • There are 3 possible • alleles for this gene.

Suggested study questions • p. 283 (1 -5, 11, 12, 17 -20)