Genetic Inheritance Chapter 20

Objectives  Predict and interpret patterns of inheritance.  Demonstrate possible results of sexually recombination with one trait and with two traits.  Dominant, Recessive,  Incomplete dominance  Codominance  Sex-linked traits

Genotype  Refers to a letter that represents the genes on a chromosome (BB, Bb)  Genes are segments on a chromosome that code for a protein trait, like hair color, eye color.  Genes are found at a particular location, discovered by Henry Morgan while studying fruit fly chromosomes in early1900s.  Alleles are one form of two genes  Brown eye, Blue eye, Green eye  One comes from mom the other from dad

Genes  Genes are codes for proteins, which give us our body traits  Genes, found on chromosomes, have 1 to 8 alleles per trait  An Allele is 1 copy of a gene on each of the two chromatids of a chromosome

We inherit half our DNA from mom and dad due to Meiosis Chromosomes inherit independently if they are on different chromosomes They inherit together if they are on the same chromosome

Phenotype  The looks that appears.

Dominant and Recessive Alleles  Dominant traits show up over recessive traits.  Dominant is represented by an uppercase letter (B)  Recessive is represented by a lowercase letter (b)  Attached earlobes is recessive (e)  Unattached or free earlobes is dominant (E)  Video Mendel Video Mendel 

Homozygous recessive  Both alleles are lowercase. (ee Genotype) Phenotype is attached earlobes

Heterozygous  Have a dominant and a recessive allele (Ee)  The recessive trait is hidden and doesn’t show up.  Phenotype is always dominant. (Free earlobes).

Homozygous dominant  Both alleles are dominant. (EE)  Phenotype is Free earlobes.

Freckles (Ff, or FF) No freckles (ff)  What is the genotype?  What is the phenotype?

Short fingers (SS, Ss) Long fingers (ss)  What is the genotype, and phenotype?

Widow’s peak hair line (Ww, WW) Straight hair line (ww)

Predicting offspring trait  If a Freckled man and a non freckled woman have a baby, what are the chances the child will have freckles?  What genotype is the father? FF or Ff  The father can give a sperm with either the F or f  What genotype is the mother? ff  The mother can give an egg with only f

Monohybrid Punnett square  Represent the mother on one side and the father on an adjacent side.  Cross the father gene with the mother gene in the squares in the second column and then the same with the third column. Ff fFfff fFfff

Chances of the offspring  Out of four possible babies, how many are Freckled, how many are not?  2 Ff, and 2 ff  2 out of 4 are freckled or 50%  This is like a coin toss. What are the chances you’ll flip heads or tails? 50% or 1 out of 2 tosses. Ff fFfff fFfff

Hybrid cross  If the man were Ff and the woman were Ff, what are the offspring chances of being Freckled?  Phenotype: 3 Freckled, 1 not freckled  Genotype: 1 Homozygous dominant, 2 Heterozygous, and 1 homozygous recessive Ff FFFFf f ff

The chances are for one gamete to produce one trait.  A 3:1 ratio is seen in a large population.  Each child has a 3:1 chance of being freckled even if the parents have had 3 babies already. 75% chance of being freckled and a 25% chance of being not freckled.

Test Cross  You can’t tell by phenotype if a person is Homozygous dominant or Heterozygous genotype. You have to do a test cross to determine the genotype.  Ff or FF?  Cross the trait with a recessive individual. Ff  If 100% of offspring are dominant then the genotype is Homozygous dominant. FF fFf f

Test cross  If half the offspring have the recessive trait then the dominant genotype is Heterozygous. Ff Ff fFfff fFfff

Math probability  Product rule: What are the chances of Freckles and Widow’s Peak? ½ x ½ = ¼ or 25%  Sum rule: What are the chances of Freckles or Widow’s Peak? ½ + ½ = 1  1 equals a sure bet it will turn out both freckles or widow’s peak.

Dihybrid cross (two traits Heterozygous)  Short hands (SS, Ss) or long hands (ss)  Widow’s Peak (WW, Ww) or Straight Hair Line (ww)

Explain Mendel’s laws of segregation and independent assortment.  Segregation: chromosomes separate during anaphase. Mendel, a monk in 1850s bred thousands of pea plants and discovered some traits disappeared in one generation and later reappeared in later generations. This he called segregation.  Independent assortment: Because these traits appeared separately from other traits, they seemed to be conserved when he cross bred pea plants, he called them independently assorted traits. Pea color was inherited independently from pea shape.  Today we know that some traits are inherited together, called sex-linked traits and like X chromosome carries the gene for baldness, or color vision.

Segregation

Polygenic trait  Height is determined by more than one allele in humans.

Codominance  Both alleles for a trait are dominant, so both traits show up.  Blood type is codominant  iAiO  iAiA  iAiB  iBiO  iBiB  iOiO

Incomplete dominance  Two alleles mix their traits, neither one is dominant or recessive.  Curly hair person with a strait haired person have babies that are wavy haired.  1:2:1 ratio  1 curly, 2 wavy, 1 straight hair

Incomplete dominance  Having too much cholesterol in blood

Hemophilia  Blood clotting disorder. Recessive.   Read page 482 to 483 of book.

X linked alleles  Color vision   Baldness  Duchenne muscular dystrophy  Fragile X syndrome  Hemophilia

Fruit fly cross 