Genetics: Heredity Flashcards
Define genotype
The genetic makeup of an organism. What alleles an organism has for a trait. Can be homozygous or heterozygous
Define phenotype
The trait that is expressed in a particular individual. How we would describe that individual (physical appearance)
Define heterozygous
Refers to an individual that has both a dominant and recessive allele for a trait (Xx)
Define homozygous
Refers to an individual that’s has two of the same allele (XX)
Define dominant trait
A trait that is always expressed in an individual
Define recessive trait
A trait that can be masked by a dominant trait and not expressed in an individual. It is only expressed in the absence of a dominant trait
Define codominance
This occurs when both alleles are dominant/fully expressed. Does not affect homozygous individuals but heterozygous individuals express both traits. Alleles are represented by different capital letters (Ex. Black birds crossed with white birds produce offspring with checkered black and white plumage, CBCW)
Define incomplete dominance
Occurs when neither of the two alleles for the same gene can completely conceal the presence of the other allele. Heterozygous individuals for this gene will have a phenotype that is somewhere between the two alleles. They are a mix (Ex. The flower colour gene in snapdragons has two different alleles: red and white, and a heterozygous individual is pink, CRCW)
Define pedigree
Flowcharts showing inheritance patterns in a family. Basically analyze how something runs in a family. They can be used for ordinary traits but are often used to track the presence or absence of an allele responsible for disease
Define F1 generation
The first filial offspring of the P-generation (parent generation)
What are autosomal chromosomes?
All chromosomes except for sex chromosomes
What are sex chromosomes?
One pair of chromosomes which determines the gender of a child. The two homologous sex chromosomes are the X and Y chromosomes
How many autosomes do we have?
44 (22 pairs)
How many sex chromosomes do we have?
2 (1 pair)
Identify all the possible genotypes for type A blood
IAIA or IAi
Identify all the possible genotypes for type B blood
IBIB or IBi
Identify all the possible genotypes for type AB blood
IAIB
Identify all the possible genotypes for type O blood
ii
State the blood type crosses in the offspring for the following pair: IAi x IAi
IAIA, IAi, IAi, ii
State the blood type crosses in the offspring for the following pair: IAIA x IAIi
IAIA, IAIA, IAi, IAi
State the blood type crosses in the offspring for the following pair: IAIB x IAIB
IAIA, IAIB, IAIB, IBIB
State the blood type crosses in the offspring for the following pair: IAi x IBi
IAIB, IBi, IAi, ii
Give the phenotype crosses of the offspring for the following pair: colour-blind dad x normal mom
Carrier female (normal phenotype), carrier female (normal phenotype), normal male, normale male
Give the phenotype crosses of the offspring for the following pair: normal dad x carrier mom
Normal female, carrier female (normal phenotype), normal male, colour-blind male
Give the phenotype crosses of the offspring for the following pair: colour-blind dad x carrier mom
Carrier female (normal phenotype), colour-blind female, normal male, colour-blind male
What is the probability of having Huntington’s disease if an Hh dad and a hh mom have 4 children?
50%
In cattle, red (RR) crossed with white (WW) create a third phenotype called roan (RW). What is this an example of?
Codominance
Perform a cross between two roan (RW) cattle and give the genotypes and phenotypes of their offspring
Genotypes: CRCR, CRCW, CRCW, CWCW
Phenotypes: red, roan, roan, white
What is a test-cross?
Used to determine the genotype of an unknown individual. If an individual has a dominant phenotype, we don’t know if they’re heterozygous or homozygous. Crossing them with a homozygous recessive will determine the genotype of the unknown individual
What would be the possible genotypes of a test-cross?
Heterozygous, homozygous recessive
In rabbits, long hair (L) is dominant to short hair (l) and black fur (B) is dominant to white (b). A heterozygous long, white-haired rabbit is mated with a short, homozygous black-haired rabbit. What are the resulting genotypic and phenotypic ratios?
Genotype: 50% LlBb, 50% llBb
Phenotype: 50% long and black hair, 50% short and black hair
Snapdragon flowers are red, pink, and white. What inheritance pattern is this?
Incomplete dominance
What is the phenotype ratio when 2 pink snapdragon flowers are crossed?
1:2:1
Red: pink: white
Which genotype has a heterozygous advantage in sickle-cell trait?
HbAHbS
Define trait
A specific characteristic or feature of an organism (Ex. Seed colour)
Define cross
Selectively fertilizing a female gamete with a specific male gamete (Ex. Cross-pollination)
Define true-breeding
Plants that can only produce offspring with that trait (Ex. Purebred green-pea plants, when self-fertillized, will only ever produce offspring with green peas)
Describe the Principal of Dominance
When an individual has the genetic information for both the dominant and recessive trait, only the dominant trait will be expressed in that individual. Therefore, you will see more dominant traits in a population than recessive
What is the Mendelian ratio?
3:1 ratio of dominant to recessive expressing offspring shown in the F2 generation when the parent generation was purebred
Describe the Law of Segregation
Even though parents have two alleles for a trait, they separate in the gametes and only one is transferred to the offspring
What is “true-breeding” or “pure-breeding”?
Breeding two individuals that are homozygous dominant or homozygous recessive
What are “hybrids” or “carriers”?
Heterozygous individuals
Give an example of a phenotypic ratio
3:1 tall plants to short plants, 75% tall and 25% short
Give an example of genotypes ratio
1:2:1 TT to Tt to tt or 25% TT, 50% Tt, 25% Tt
Describe the Mendellian Genotypic Ratio
When crossing two heterozygotes, the genotypic ratio is always going to be 1:2:1 for the genotypes homozygous dominant: heterozygous: homozygous recessive
What are the phenotypes of the F1 offspring of two individuals, purebred for two traits?
All will express dominant traits
What are the phenotypes of the F2 offspring of two individuals, purebred for two traits?
9 displaying dominant forms in both traits, 3 displaying one dominant and one recessive, 3 displaying the other dominant/recessive pair, 1 displaying both recessive forms
Describe the Law of Independent Assortment
The inheritance of one trait has no effect on the inheritance of another. The alleles for one gene segregate independently of the alleles for another of the chromosome
Define autosomal recessive disorder
A disorder caused by a recessive autosomal allele. Only appears in homozygous individuals. Most genetic disorders are this type (Ex. Cystic fibrosis)
Define autosomal dominant disorder
A disorder caused by a dominant autosomal allele. Individuals only need one copy of this allele to express the disorder (Ex. Huntington’s disease)
List the symbols of a pedigree
Square - male
Circle - female
Diamond - sex unknown
Square/circle with a line through it - deceased individual
Black square/circle - affected individual
Circle with black dot in it - carrier
Square and circle connected laterally - marriage
Squares/circles connected from top - twins
Describe sickle-cell anemia
A disorder that causes a misshapen red blood cell than inefficiently moves oxygen. It is controlled by a gene with codominant alleles. HbA represents the allele for normal shaped red blood cells, HbS represents the allele for sickle cell anemia.
HbAHbA individuals are normal
HbSHbS individuals have sickle cell anemia
HbAHbS have sickle cell trait, so they are immune to malaria but do not have sickle cell anemia (heterozygous advantage)
Define multiple allele inheritance
When a single gene has more than two possible alleles, it increases the possible genotypes and phenotypes (Ex. Rabbit coat colour has four alleles. They are listed in order of dominance: agouti (C) > chinchilla (Cch) > Himalayan (Ch) > albino (c))
Define polygenic inheritance
This occurs when multiple genes are controlling a single trait. Traits controlled like this are called polygenic traits. These traits exhibit continuous variation meaning there is a broad spectrum of possible phenotypes (Ex. Skin colour, length of ears of corn)
Describe environmental effects on genes
Sometimes genes can be turned on or off in the cells of the body based on the environment around the organism (Ex. Himalayan rabbits have a gene for dark fur that only gets turned on when it is below a certain temperature)
Define linked traits
Traits close together on the same chromosome that tend to be inherited together. All of the genes on the same chromosome are called a linkage group. In meiosis I during crossing over, some of these genes can become unlinked/broken but infrequently. Linked genes most likely account for such phenomena as red hair being strongly associated with light complexioned skin among humans. If you inherit one of these traits you will most likely inherit the other
What determines whether linked genes will separate during crossing over?
The further apart the genes are from each other in a chromosome, the greater the likelihood that they will be unlinked as a result of crossing-over. Likewise, genese located closer to the ends, rather than in the middle, of a chromosome are more likely to be recombined during meiosis
How many genes do the X and Y chromosome carry?
X carries about 2000 genes and the Y has fewer than 100
Give an example of an X-linked and Y-linked trait
X-linked: colour blindness, hemophilia, baldness
Y-linked: hairy ears in males
Give an example of an autosomal recessive disorder, autosomal dominant disorder, X-linked trait, and Y-linked trait
Autosomal recessive: cystic fibrosis
Autosomal dominant: Huntington’s disease
X-linked recessive: hemophilia, colour blindness
Y-linked: hairy ears
Give an example of incomplete dominance, codominance, multiple allele inheritance, and polygenic inheritance
Incomplete dominance: flower colour gene in snapdragons
Codominance: black and white birds, roan cows
Multiple allele inheritance: rabbit coat colour
Polygenic inheritance: skin colour, length of ears of corn, human height
