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Chapter 5Basic Genetics
GCA General BiologyMr. Cobb
Mendel’s Genetics
Monk
Worked with pea plants
7 traits
Mendel’s Concepts
Unit Characteristics
Dominant and Recessive
Law of segregation
Unit Characteristics
Traits are caused by factors that occur in pairs.
He represented these with letters.
T = tall
t = short
Dominant & Recessive
Dominant gene hides a recessive gene.
TT = Tall plant
Tt = Tall plant
tt = short plant
SegregationWhat does Segregate mean?
When a cell forms gametes genes separate.
Only 1 factor for each trait will be in each gamete.
He had figured out Meiosis, but did not know why or how.
TerminologyPhenotype = physical appearance
Genotype = the specific genes
allele = an alternate form of a gene (purple flower allele or white flower allele)
Homozygous = both alleles are the same
Heterozygous = alleles for a trait are different.
Punnett SquaresUse to determine the probability of an outcome.
25% both heads
50% heterozygous
25% both tails
Punnett Square
Free earlobes = F
Attached = f
What is phenotype and genotype?
Punnett SquareResults are expressed in ratios pg. 116
homozygous dominant: heterozygous: recessive.
Cross two heterozygous for trait P, what is the genotypic ratio.
P is for purple and p is for yellow, what is the phenotypic ratio?
Test CrossIf you corn that shows the dominant purple kernels (P), then what is the genotype?
PP or Pp, it could be either.
Do a test cross and mate with corn that is yellow recessive because that genotype is pp.
If any of the offspring show the recessive trait, then the unknown was heterozygous.
Variations of MendelIncomplete dominance = one trait is not completely dominant over the other, so they “blend”. Red flower + White flower = pink
Variation (continued)codominance = both alleles are expressed, but there is no blending.
Variation (continued)Multiple alleles = More than two alleles in the population. Blood type
Blood TypeA and B Blood Types are both Dominant and notated by IA and IB.
The recessive is not having the antigens and it is notated as i.
A person with A blood type could be IAIA or IAi
AB Blood type is IAIB.
Read the box on top of page 121. Did a mixup happen?
Dihybrid Crosses
Same as Punnett Square, but now we are looking at the probability of two traits together
Our example is pod color and is the pod constricted (skinny) or inflated (fatter).
Dihybrid Cross
When would this be useful in society?
Independent Assortment
The separation of one allele does not affect the other alleles.
For example, the pod color does not affect the pod shape or flower color.
These alleles are sorted independently of each other.
Independent Assortment
The “G” Chromosome is independent from the “I” chromosome.
Polygenic Inheritance
2 or more genes working together result in a single trait.
Human traits like hair color, skin color, eye color, height.
The example in the book is the comb of chickens.
PleiotrophyJust FYI
Pleiotrophy is one gene controls many characterisitics.
Example is sickle cell anemia and affects 1 in 12 black people in the U.S.
Sickle cell anemia causes the red blood cell to sickle in high elevation and in activity.
Sickle Cell Anemia
Ryan Clark of Pittsburgh can not play in Denver due to sickle Cell Anemia.
Sickle Cell Anemia Red Blood Cells
Sex ChromosomesChromosomes that determine the sex of an individual.
The autosomes are the other 22 chromosomes.
XX is a female
XY is a male
Sex Chromosomes
The male donates the Y chromosome. So the male determines the sex of the offspring.
Sex Chromosomes
There are traits on the chromosomes and these are called sex-linked traits.
Hemophilia - blood does not clot correctly
baldness
color blindness
Sex Chromosomes
Males usually exhibit the traits. Why?
Males only have 1 X chromosome and females have 2 X chromosomes.
Males will exhibit the recessive trait.
Color Blind Test
Color Blind Test
Color Blind Test
Pedigree
A chart used to track a genetic trait through a generations.
This is a pedigree of hemophilia in the British Royal Family.
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