FCAT Review 12 – Heredity & Genetics

Traits – physical characteristics of an organism Heredity – the passing of traits from parents to offspring Traits – physical characteristics of an organism *This is why offspring look like their parents Let’s take a look at some examples.

*Hair color *Eye color *Toe length *Widow’s Peak *Hitchhiker Thumb

*Traits are found in genes (passed from parent to offspring) within the cell’s nucleus

*Genes are part of DNA (Deoxyribonucleic acid) *DNA - material that contains all the different genes *Double Helix – the structure of DNA resembles a twisted ladder

*DNA is strung together in long strands called Chromosomes *There are 23 pairs of chromosomes in each cell *DNA is the blueprints for building cells, tissue, organs, and the organism

Cell Division

Mitosis *The process where cells (parent cells) reproduce duplicate cells (daughter cells) Muscle cells produce new muscle cells, bone cells produce new bone cells, etc.

Meiosis *The process of reproducing sex cells

MITOSIS MEIOSIS

father mother How are chromosomes, genes, and inheritance related? The human body has ____ chromosomes in each cell *23 pairs 46 A baby gets 23 chromosomes from their ________ and 23 from their ________ *Total - 46 father mother

Why don’t offspring always look exactly like their parents then?

*Genes and Alleles -genes control the inheritance of traits -alleles are the different forms of a gene (traits) from each parent

*Genes and Alleles *Trait - Plant Height Alleles: Tall Plant Short plant

*Genes and Alleles *Dominant allele- trait that always shows up in an organism when its present Tall Plant (T)

*Genes and Alleles *Recessive allele – the trait is hidden when the dominant allele is present (Lower case letter) Short plant (t)

Phenotype and Genotype Phenotype – the physical appearance, or traits, of an organism *Brown Hair, Black hair *Right handed, left handed *Tall, short

Phenotype and Genotype Genotype – the genetic makeup, or combination of alleles, of an organism Hair color: Brown Hair (B), Black Hair (b) Brown hair – BB, Bb Black hair - bb

Phenotype and Genotype Trait – Handedness Phenotype – Right handed (R), left handed (r) Genotype – RR, Rr, rr

Alleles for Rabbit Ears: Straight - dominant (S), Floppy - recessive (s) Phenotypes Genotypes SS Ss ss

Alleles for Guinea pig fur color: Brown – dominant (B), White – recessive (b) Phenotypes Genotypes BB Bb bb

Alleles for Skin Complexion: Clear – dominant (C), Freckled – recessive (c) Phenotypes Genotypes CC Cc cc

Homozygous & Heterozygous Alleles Homozygous – organism with 2 identical alleles for a trait (BB, DD, rr) *Purebred Heterozygous – organism with 2 different alleles for a trait (Bb, Dd, Rr) *Hybrid

Alleles for Rabbit Ears: Straight-dominant (S), Floppy-recessive (s) Phenotypes Genotypes Homozygous or Heterozygous SS Homozygous Ss ss

Alleles for Guinea pig fur color: Brown – dominant (B), White – recessive (b) Phenotypes Genotypes Homozygous or Heterozygous BB Homozygous Bb Heterozygous bb

CC Cc cc Alleles for Hair type: Homozygous Heterozygous Curly – dominant (C), Straight – recessive (c) Phenotypes Genotypes Homozygous or Heterozygous CC Homozygous Cc Heterozygous cc

How are chromosomes, genes, and inheritance related? The alleles from the female and the alleles from the male combine together in one of ___ possible combinations 4 A ________________ shows what these possible combinations can be Punnett Square

Punnett Square A chart that shows all the possible ways alleles can combine in a genetic cross.

A rabbit with straight ears (Ss) breeds with a rabbit with floppy ears (ss). What are the probable outcomes for the offspring? S s S s s s s S s s s s

s S S s s s s S s s s s Combinations: Ss = 2 ss = 2 Possible = 4 Straight ears (S) = 2 of 4 (50%) Floppy Ears (ss) = 2 of 4 (50%) s S S s s s s S s s s s

Example – Clear skin (C) is dominant to freckled skin (c) Example – Clear skin (C) is dominant to freckled skin (c). What is the probability that an offspring will have freckles if both of their parents have clear skin (Cc)? *Set up a Punnett square to answer this. Answer = 25%

Example – Brown hair (B) is dominant to blonde hair (b) Example – Brown hair (B) is dominant to blonde hair (b). What is the probability that an offspring will have blonde hair if one parent has brown hair (BB) and one parent has blonde hair (bb)? Answer = 0%

Example – The male sex trait (Y) is dominant to the female sex trait (x). The male sex trait is heterozygous (Yx) and the female sex trait is homozygous (xx). What is the probability a child is born male or female?

x x Mother Father Y Yx Yx xx xx x y = male x = female xx xx x There are ___ of 4 chances the baby will be male and ___ of 4 chances the baby will be female (50 % / 50 %) 2 2