Genetics and Heredity Mitosis Review Occurs in Somatic

Genetics and Heredity

Mitosis Review • Occurs in Somatic Cells (regular body cells) • Cells are diploid (2 of each chromosome) • This is asexual reproduction • One parent produces two daughter cells • All are identical!!!

Asexual Reproduction • One parent • Offspring are identical to parent/ No genetic variation • Examples: Vegetative propagation, budding, cloning • Why is this beneficial? – Fast – If it is not broke, don’t fix it!

Sexual Reproduction • Two parents • Offspring are different from parents • Genetic Variation • Why is this beneficial? – Produces new traits that can help offspring survive.

• Diploid – A cell with two of each chromosome (2 n) • Haploid – A cell with one of each chromosome. (n) • Meiosis – Process that reduces the number of chromosomes to half the number in the original cell. – Produces haploid cells called gametes. – Occurs in sex cells (gametes) – Cells are haploid (chromosome # is cut in half) – Sexual reproduction – Produces 4 cells that are different

Mitosis Meiosis

The Law of Independent Assortment states that the chromosomes in a cell will separate (sort) themselves differently each time egg and sperm are formed. This means no siblings are alike unless they are identical twins!!

What happens after gametes are formed? ? • Fertilization – Gametes join to create a diploid cell with a full set of chromosomes. – Sperm and Egg form a zygote. • Does this happen in plants and fungus? ? ?

Karyotypes / 3. 2 • Karyotypes are pictures of a person’s chromosomes. You can see all 46 chromosomes. • Normal human karyotypes have 46 chromosomes or 23 pairs. • 22 pairs are autosomal chromosomes 1 pair are the sex chromosomes – Females XX – Males XY

Chromosomes and karyotypes • Humans have 46 chromosomes in every cell of their body. Those 46 chromosomes are actually 23 pairs of chromosomes. • 23 come from Mom’s egg • 23 come from Dad’s sperm • Remember meiosis? ? ?

Chromosome Abnormality - Nondysjuctions • Change in a persons chromosomes. • Chromosomes can be broken, deleted or added. – Remember: There is a lot of DNA in one chromosome. Chromosome mutations can affect MANY genes. • Caused by nondisjunction: chromosomes do not separate correctly during meiosis.

Examples of Chromosomal Abnormalities • Downs Syndrome – Caused by: Nondisjunction/Trisomy – Characteristics: Facial differences, heart defects, mental delays – Trisomy 21 • Turner’s Syndrome – Caused by: Nondisjunction/Monosomy – Monosomy of the sex chromosomes – X ___ • Klinefelter’s Syndrome – Caused by: Nondisjunction/Trisomy – Trisomy of the sex chromosomes – XXY

Detecting Chromosomal Mutations • Pre-natal – Amniocentesis: remove a sample of the amniotic fluid surrounding the fetus. – Chorionic Villi Sampling: Sample tissue near the placenta. • These can be used to create a karyotype.

Gregor Mendel • Research on heredity-passing of characteristics from parents to offspring. • Studied science and statistics. • Based most of his studies on peas plants. • Observed characteristics of pea plants: – Plant height: long or short – Pod color: green or yellow – Seed structure: smooth or wrinkled – Seed color: yellow or green – Flower color: purple or white

What did Mendel observe? • When he planted seeds from purple flowering plants some offspring had purple flowering plants and others had white flowering plants. • When he planted smooth seeds he had plants that produced smooth seeds and some plants that produced wrinkled seeds.

• Mendel discovered there were 2 forms of each trait/gene. Each form of a trait or gene is called an allele. Each parent gives one allele for each trait. So individuals have two copies. • Mendel began to realize that one allele could “cover up” the other allele. • Dominant and recessive alleles. One allele is dominant and is always expressed One allele is recessive and is “covered up” by the other • How/When do we get these traits? – Law of segregation: a pair of factors is separated during gamete formation. – This means: Alleles for each gene separate to different gametes during meiosis.

• The traits you express are your phenotype. • Alleles show your genotype. The actual genetic make-up. (letters) Relationship between genes and alleles • A gene is the DNA that codes for a characteristic. The alleles are the versions of that trait. Ex. Plant Height (trait/gene) T=Tall, t=short (alleles) Flower Color (trait/gene) P=purple, p=white (alleles) • Always use ONE letter to represent a gene. Use capital letters for dominant, lower case letters for recessive.

• Homozygous (“homo” means same)- genotype where the organism has two of the same alleles for a trait. – Pure-breeding or True-breeding – TT or tt • Heterozygous (“hetero” means different)-genotype where the organism has two different alleles for a trait. – Hybrid or Carrier – Tt • When alleles are combined they may or may not be expressed (shown) • Dominant traits are always expressed. • Recessive traits are sometimes expressed. Only when the organism has two recessive alleles. Homozygous recessive.

• Rabbits – B: Big Feet, b: small feet – F: Floppy ears, f: straight ears – Bk: Black rabbits (dominant), Br: Brown rabbits • Show the F 1 generation of a monohybrid cross between a rabbit that is homozygous for floppy ears and a heterozygous rabbit.

• Cross-offspring from two parents – Monohybrid looks at one trait • • P generations-parents F 1 generation-first offspring from parents F 2 generation-offspring from F 1 Selfed/Self-fertilization-cross with one just like itself • Test Cross-figure out an unknown genotype

• Green pod color in peas is dominant to yellow pod color. What offspring are possible from a cross between a GG plant and a Gg plant? • B represents black feathers and b represents white feathers in wrens. What are the possible genotypes and phenotypes of the F 1 from a cross between a homozygous black wren and homozygous white wren? • Deafness in dogs is caused by a recessive allele. A deaf dog is crossed with a hearing dog and some of the puppies are deaf. Write the genotypes of the parent dogs. • A woman is a carrier for the disease PKU. Her husband is healthy. What are the chances they will have a child with PKU?

Types of Dominance • The type of dominance we have been studying is complete dominance. – Two phenotypes are possible. • Incomplete dominance: When the F 1 generation could have a phenotype completely different from the parents. – Three phenotypes are available for each trait. The third phenotype is a mix of the other two. – Example • Codominance: When the F 1 generation could have a phenotype completely different from the parents. – Three phenotypes are available for each trait. The third phenotype shows both of the other two. – Example

Practice • Complete Dominance A-D • Incomplete Dominance E • Codominance F • U 5 HW 2 #1 and #2

• Polyallele Traits (Multiple Allele) – Several possible alleles for one trait. – Results in 4 -5 phenotypes – Ex. Blood Types (polyallele and codominance) – Blood Type Chart and practice in your notes. • Polygenic Traits – Characteristics controlled by two or more genes. – Genotype: Tt. GGEe – Phenotype: More dominant alleles = the more extreme of a trait. – Ex. Eye color is determined by the combination of approx. 3 genes.

Sex-linked Trait • Last set of notes in Types of Inheritance!!!

• Sex Linkage (these are complete dominance) – X-linked: genes located on the X chromosome – Y-linked: genes located on the Y chromosome – The presence of a gene on a sex chromosome is called a sex-linked trait • Ex. Eye color is an X-linked trait in fruit flies. Red is the dominant allele for this trait. Therefore white eyed females will only produce white eyed male offspring. • Hemophilia is an X-linked recessive trait. Show the punnet square between a normal male and a female who carries the trait for hemophilia. What are the chances they will have a child with hemophilia?

• Add the activity sheet to your notes and complete. (10 minutes) • Work on U 5 HW 2 and Vocabulary • Pull up/ Print Study Guide for Monday.