Chapter 7 Genetics
Gregor Johann Mendel
1) Austrian Monk 2) Bred pea plants and observed their outcomes 3) He discovered patterns of inheritance that now form the current study of genetics
Mendel's theory of Hereidty
1) There are different versions of genes. 2) When two different alleles are inherited together, one may be expressed, while the effect of the other may be silenced. 3) For each characteristic, an organism inherits two alleles, one from each parent. 4) When gametes are formed, the two alleles of each gene are separated.
The Principle of Dominance
1) one gene in a pair masks the other from being expressed
7 main characteristics Mendel studied
1) seed texture (round or wrinkled) 2) seed color ( yellow or green) 3) seed coat color (white or colored) 4) pod appearance (inflated or constricted) 5) pod color (yellow or green) 6) position of flowers (axial or terminal) 7) plant height (tall or short)
Why did Mendel use pea plants in his studies?
1) several observable traits 2) both male and female parts 3) it grows quickly
A flower exhibits incomplete dominance. If one flower is red and one is white, what is the probability of their offspring becoming pink?
100% *All pink
P x P
F1
The results of a cross of the parental generation.
F1
What did Mendel call the offspring of the P generation?
F1 (1st Filial generation)
F1 x F1
F2 (2nd Filial Generation)
A cross in which the phenotype is a blend or is in between the two alleles
Incomplete Dominance
A cross between organisms involving only one trait
Monohybrid Cross
How do the Punnett squares for a monohybrid cross and a dihybrid cross differ?
Monohybrid: involves only one trait Dihybrid: involves two traits
Traits determined by two or more alleles.
Multiple alleles
_____ _____ are responsible for traits such as hair color, eye color, height, and weight
Multiple alleles
A classmate tells you that a person can have a type AO blood. Do you agree? Explain?
No, AO blood type is not possible
Blue eyes (b) is recessive to brown (B) eyes. Cross a heterozygous brown-eyed dog with a blue-eyed dog. What are the resulting genotypic and phenotypic ratios?
P ---> 2:2 G ---> 0:2:2
Tall (T) is dominant over short (t) in corn. Cross a homozygous tall plant with another plant of the same genotype. What are the resulting genotypic and phenotypic ratios?
P ---> 4:0 G ---> 4:0:0
The letters outside the boxes in a Punnett square represent _____ _____.
Parents' alleles
An observable trait - what you see
Phenotype
When two or more genes affect a trait
Polygenic Inheritance
The fraction or percentage that describes the likelihood of an event occurring.
Probability
A diagram that shows possible outcomes of a genetic cross
Punnett Square
Pedigree that skips a generation (one generation missing affected)
Recessive
The allele in a pair that does not affect the trait
Recessive
The sex linked allele is located on the __ _____.
X chromosome
Non-carrier Female
X^H X^H
Carrier Female
X^H X^h
Normal Male
X^H Y
Female with hemophilia
X^h X^h
Male with Hemophilia
X^h Y
Is it sometimes possible to tell a person's genotype by their phenotype?
Yes
A sample of peas contains 600 green peas and 200 yellow peas. a) what proportion of peas are green? b) What is the ratio of green to yellow peas?
a) 3/4 b) 3/1
Law of Independent Assortment
alleles of different genes separate independently of one another during gamete formation
Genotype
an organism's genetic make-up ex. BB, Bb, bb
Phenotype
an organism's physical appearance ex. brown eyes
autosome
any chromosome of that a sex chromosome
Universal donor
can donate blood to anyone (Type O)
Universale acceptor
can receive blood from anyone (Type AB)
Sex-linked traits
carried on the X chromosome *usually RECESSIVE - effects usually only seen in males
sex chromosome
chromosome that determines the sex of an organism
hybridization
cross between two individuals that have different traits
testcross
determine the organism's genotype
Heterozygous
different alleles for each trait
Alleles
different forms of a gene; come from your parents; different alleles for each zygote
Trait
heritable variant of a genetic character
Codominance
heterozygous offspring express BOTH phenotypes of the parents
In order for a recessive trait to be expressed, the genotype must be _____ recessive.
homozygous
Type O
ii
Monohybrid Cross
involves only one trait
Dihybrid Cross
involves two traits
Genes
located on chromosomes
Sex-linked disorders occur more commonly in _____.
males
True-breeding
organisms that are pure for a trait
Cross-breeding
placing pollen from one pure plant onto the stigma of another pure plant
Hemophilia
sex-linked recessive trait *a defective gene reduced the blood's ability to clot properly
Dominant
the expressed gene - Capital letter
Recessive
the masked gene - lowercase letter
Homozygous
the same allele for a trait
Polygenic Inheritance
traits inherited from a combination of genes - several genes influence a trait - affect things such as height, eye color, skin color, hair color
Law of Segregation
two alleles for a trait segregate (separate) during gamete formation (meiosis)
Incomplete Dominance
when the F1 generation shows a phenotype in between that of the parents *Genotype is always heterozygous
The offspring exhibits both traits
Codominance
Parental generation
"P"
Pedigree
- only recessive traits can skip a generation - If homozygous dominant, ALL offspring will display the trait - If the trait skips a generation, both parents are heterozygous
If having brown eyes is dominant, show how two parents with brown eyes could have children with blue eyes using a monohybrid cross. What are the odds (%) of this happening?
25%
Complete dihybrid cross with all traits heterozygous. Phenotypic ratio? ex. FfEe x FfEe
9:3:3:1
IF BOTH PARENTS ARE HETEROZYGOUS FOR BOTH TRAITS... PHENOTYPIC RATIO IS
9:3:3:1
The alternative forms of genes
Alleles
Blue (B) is dominant to white (b) in flowers. What is the genotype for a plant that is heterozygous? What would be its phenotype?
Bb P ---> Blue
_____ are heterozygous for a disorder, but do not exhibit the disorder
Carriers
A cross involving two traits rather than one
Dihybrid cross
In a heterozygous individual, what allele is expressed?
Dominant
Pedigree that has affected trait presented throughout
Dominant
The allele of the pair that seems to affect the trait. Shows up
Dominant
The study of heredity
Genetics
The genetic makeup of combination of alleles.
Genotype
Who is the "father of modern genetics?"
Gregor Johann Mendall
An individual with two alleles for a trait being different
Heterozygous
An individual with two alleles the same for a trait
Homozygous
The offspring of two different purebreds
Hybrid
Type AB
I^A I^B
Type B
I^B I^B or I^B i
Type A
I^a I^A or I^A i
Any gene located on the sex chromosomes.
Sex-linked trait
Which blood types are not possible for children of two parents with type AB blood?
Type O
