Unit 6 Haploid vs Diploid Mitosis creates Diploid

Unit 6

Haploid vs Diploid • Mitosis creates Diploid cells, which are cells that contain two complete sets of chromosomes. • We abbreviate this 2 n.

Haploid vs Diploid • In a Haploid cell, only ONE complete set of chromosomes is present. • We abbreviate it n.

Meiosis • Meiosis is sexual reproduction. Only occurs in the sex organs – ovaries and testes. • Results in the production of gametes, which are sex cells. • Meiosis begins with a diploid cell, and the end result is 4 haploid cells. • Meiosis is similar to Mitosis because there is still Interphase and PMAT, but in Meiosis, PMAT occurs twice.

Stages of Meiosis • Interphase • The DNA replicates • MEIOSIS I • Prophase I • Spindle fibers form and the chromosomes pair up. • These paired chromosomes are called Homologous Chromosomes. • While the Homologous Chromosomes are paired up, crossing over occurs.

Crossing Over • During crossing over, genetic information (DNA) is exchanged. • The result is chromatids that are no longer identical.

Meiosis I • Metaphase I • The homologous chromosomes line up in the cell. • Anaphase I • The chromosomes pull apart.

Meiosis I • Telophase I • The cells begin to divide into 2 cells. • Cytokinesis • 2 individual, haploid cells are created.

Meiosis II • Prophase II • Chromosomes form, spindle fibers form • Metaphase II • Chromosomes line up

Meiosis II • Anaphpase II • Sister chromatids pull apart • Telophase II • The 2 cells are now dividing into 4

Meiosis II • Cytokinesis • 4 haploid cells are formed. All are genetically different.

Gamete formation in males Stages of Meiosis Gamete formation in females

Meiosis Video https: //www. youtube. com/watch? v=to. WK 0 f. Iy. Fl. Y

Genetic Variation • How do we each become our own individual with our own unique set of genes? How does genetic variation occur? • Genetic variation occurs during crossing over (Prophase I)

Genetic Variation cont. • Occurs during random assortment of chromosomes during the different stages of meiosis. • This is the Law of Independent Assortment.

Genetic Variation • Law of Segregation – during meiosis, the chromosome splits and the chromatids segregate. • Each gamete gets half of the genetic information.

Genetic Variation cont. • Occurs during fertilization – ½ of DNA comes from each parent • Gene mutation • Non-disjunction – chromosomes did not properly split

Stop here day one

Karyotype • A karyotype is a picture or profile of a person’s chromosomes. • Chromosomes are paired up and numbered 1 -22, and the 23 rd chromosome is labeled XY and determines gender. • We use karyotypes to show chromosomal abnormalities.

What can you notice about this Karyotype – what is it missing? On the X and Y chromosomes, there is only 1 X chromosome. It is missing a second sex chromosome. This is called Turner’s Syndrome.

This is a Karyotype for Trisomy 21. Notice there are 3 chromosomes on the 21 st chromosome. This was caused by a non-disjunction. Trisomy 21 is also known as Down Syndrome.

More practice with karyotypes • Open your textbook to…Pg. 318 • Chromosomes for Male ? Female? • Pg. 329 • Male of Female? • Normal or not? • Pg. 335 • Male or Female?

Gregor Mendel • Father of genetics • Austrian Monk • He did experiments on Pea plants to show traits were passed down • He studied the shape, seed color, outer coat, pea pod, and stem to see which traits occurred more or less often. • He was the first to observe: • The Law of Independent Assortment • The Law of Segregation

Genotype • The genes of the organism Phenotype • What the organism looks like

• Allele – one or more versions of a gene. • Located at a specific position on a specific chromosome • Dominant Allele • What will be expressed. • It “masks” other alleles. • Written in upper case. • Recessive Allele • It will only be expressed if the dominant allele is not present. • Written in lowercase.

• Heterozygous • Hybrid • Having 2 different alleles for a gene • Homozygous • Same; purebred • Have 2 of the same alleles for a gene

Punnett Squares • The diagram used to predict the genotype and phenotype.

Punnett Squares • Ex. You have 2 mice that are heterozygous for their brown coats. Brown is the dominant color and white is the recessive. Create a Punnett Square that shows the cross between these two mice. B B BB b Bb What are the ratios of genotypes you will get? 1: 2: 1 bb What percent of each phenotype will you see? 75% brown 25% white

Incomplete Dominance Punnett Square

Incomplete Dominance • When one allele is not completely dominant over the other. • The heterozygous genotype will result in a blend. • Ex. Snapdragons

Co-dominance • Co-dominance results in the expression of both traits.

Polygenic Traits • Traits which are coded for by more than one allele. • Usually results in blending of traits. • Ex. Hair color, eye color, skin color

Blood Types • Blood types are an example of codominance. • A and B are both dominant. • O is recessive.

Sex-Linked Traits • Trait is more likely to be inherited by males. • Recessive • Genes for these traits are found on the X and not the Y chromosome. • This is why the X is bigger than the Y.

Sex-Linked Traits

Examples of Sex-linked Traits • Red/Green Colorblindness • Hemophilia – the inability of the blood to properly clot

Pedigrees • Charts are made to show traits are passed down through the generations. • Things to note: • Generations are denoted by Roman numerals. • Number individuals from left to right.

Pedigrees • Symbols: Female Married Divorced Male Affected Male Deceased Siblings

Hemophilia in the Royal Family

Bellwork • From Genetics practice problems, finish the page on Blood Type Punnett Squares • Finish reading and answering questions on blood types

What else can Punnett Squares be used for? • Punnett Squares can also be used to show genetic disorders get passed down from parent to offspring. • PKU is a recessive gene. • Ex. Phenylketonuria (PKU) • A genetic disorder that causes the build up of the amino acid phenylalanine in the body. • Symptoms: delayed development Intellectual disability P p Behavioral, emotional and social problems Psychiatric disorders P PP Pp Neurological problems that may include seizures Hyperactivity Poor bone strength p Pp pp Skin rashes (eczema)

Genetic Disorders • Cystic Fibrosis • Most commonly caused by a deletion of 3 base pairs on the 7 th chromosome. • Approx. 2500 babies are born each year in US with Cystic Fibrosis. • It is estimated that 10 million Americans are carriers of the gene. • Recessive • Symptoms: Respiratory problems Mucous in the lining of the lungs

Genetic Disorders • Huntington’s Disease • Dominant Trait • Caused by a mutation on the 4 th chromosome • Approx. 1 in 30, 000 people in US have Huntington’s • Symptoms: • Affects thinking, motion, and movement • Symptoms do not usually appear until age 30 -50

Genetic Disorder Chart Genetic Disorder Recessive, Dominant, or Chromosome Affected Symptoms/Traits