Transcript Genetic Inheritance

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
 https://www.youtube.com/watch?v=Mehz7tCxjSE
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.
F
f
f
Ff
ff
f
Ff
ff
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%
F
f
f
Ff
ff
f
Ff
ff
 This is like a coin toss. What are the chances you’ll flip heads or tails? 50% or
1 out of 2 tosses.
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
F
f
F
FF
Ff
f
Ff
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
F
F
f
Ff
Ff
f
Ff
Ff
 If 100% of offspring are dominant then the genotype is Homozygous dominant.
Test cross
 If half the offspring have the recessive trait then the dominant genotype is
Heterozygous. Ff
F
f
f
Ff
ff
f
Ff
ff
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.
 https://www.youtube.com/watch?v=bmQwMllhCUM
 Read page 482 to 483 of book.
X linked alleles
 Color vision
 https://www.youtube.com/watch?v=F7jWCbwago0
 Baldness
 Duchenne muscular dystrophy
 Fragile X syndrome
 Hemophilia
Fruit fly cross
 https://www.youtube.com/watch?v=b4mMD4xzfn4