Lesson 10- Cell Division and Genetics (43-76) Flashcards
True Breeding
Breeding between two parents that are homozygous for genes meaning they create the 3:1 offspring
Phenotype
The trait shown in the offspring, its physical appearance of trait
Genotype
Genetic makeup (alleles) that determine the physical appearance
The alles the offspring demonstrates
(PP,Pp,pp)
Most traits are determined by allele pairs
Ex: widows peak (dominant) Brown eyes (dominant) over blue
Homozygous vs Hetrozygous
The type of alles shown
Homozygous = PP,pp (dominant or recessive). Same genes
Heterozygous = Pp (mixed). Different genes. Dominant trait is displayed
Punnett square
Determines the probability of inheriting a trait
Compares alleles from both parents
Dominant traits
TT x TT = 100% with trait
TTxTt
-100% with trait
- 50% heterozygous
TTxtt
-100% with trait
-100% heterozygous
tt x tt = Trait not shown
Heterozygous parents
Tt x Tt and if dominant
75% with trait
- Homozygous dominant and
heterozygous
-25% no trait
-50% heterozygous
Recessive disorders
Most disorders are recessive
Recessive disorders
-Show up only in individuals homozygous for the allele
Carriers
- heterozygous individuals
* carry the recessive allele but are phenotypically normal
Ex: Cystic Fibrosis
Sickle cell anemia
Dominant Genetic disorders
Disorder expressed if dominant gene is present, seen in heterozygous indiviudals
75% instead of 25%
Example: Huntington disease
-effects seen after 40 and neurogenertive
Pedigree Analysis
A Pedigree:
-Family tree that describes the interrelationships of parents and children across generations
-Inheritance patterns of traits can be traced
Can trace back dominant or recessive traits
Codominance
Two dominant alleles each distinctly affect the phenotype
- More than 2 allele forms
E.g. Human blood
groups
Both A and B phenotypes are dominant
Dominance vs prevalence
Domiants vs most common trait seen
Incomplete dominance
Phenotype of F1 offspring is between the phenotypes of the two parental varieties.
Ex flowers: red and white to pink
Human example:
Eye/hair/skin colour?
Sickle-cell anemia
* Heterozygous people can
show mild symptoms
Pleiotropy
Where one gene has multiple phenotypic effects
1 amino acid that’s gone wrong
Polygeny
When traits are determined by two or more genes
Many human characters
-Vary along a continuum
-called quantitative characters
skin colour is an example: melanin has two types, dark and yellow
Sex linked traits
if a mother is heterozygous for a recessive trait
-50% of daughters will be carriers
-50% of sons will have the recessive trait
Punnet square
Ex: colourblindness
Hemophilia
Baldness
Sex linked genes
The chromosomes carries genes unrelated to the sex
-Males x and y
-females two x
Male have two possibilities: y and a dominant or reccesive x
Female have three: homozygous dominant x, heterozygous x and homozygous recessive x
Sex linked disorder
Most are recessive and affect males
-A male who has a single X linked allele from his mothe, will have the disorder if he has the allele
- A female who has two x alleles needs recessive allele from both parents for diseases (rare)
Gene expression
Having a gene does not mean its expressed
Epigenetic effects
- Histones or methylation
- Can turn on or off gene expression
- external factors determine epigenetic
Human diseases
Have both genetic and environment components
Ex; heart diseases and cancer
Lifestyle choices matter, stuff like smoking may increase risk
Character and trait
Character: a heritable feature, such as eye colour or hair colour
Trait: a variant of a character, such as blue eyes or brown eyes
Generations
P generation – the true-breeding parents
F1 generation - hybrid offspring of the P generation
F2 generation –when F1 individuals self-pollinate
Alleles and Locus
Alleles – inherited character on the genes (get one from each parent)
Locus – location on the gene
