Lecture 10/11 & 10/13: Genetics
What is the genotypic ratio?
1 PP: 2 Pp: 1 pp
What is the phenotypic ratio for pea traits (flower color)?
3 purple: 1 white
What is the phenotypic ratio?
3:1 ratio
What is the ratio for a typical dihybrid cross between two heterozygous when two genes are on different chromosomes?
9:3:3:1
How many alleles may a given gene have?
>2.
What is a recessive condition?
A condition that is only seen if a genotype is homozygous recessive
What is a punnett square?
A diagram that is used to predict an outcome of a particular cross or breeding experiment
What is co-dominance?
A form of dominance in which the alleles of a gene pair in a heterozygote are fully expressed thereby resulting in offspring with a phenotype that is neither dominant nor recessive
What is the Barr body?
A small, densely staining structure in the cell nuclei of female mammals, consisting of a condensed, inactive X chromosome
What is an autosomal recessive trait?
A trait that will only be acquired if both recessive alleles are defective.
What is a pedigree?
A tree through which genetic traits can be tracked. Follows traits through generations.
What is methylation?
Addition of CH_3
What is epigenetics?
Any process that alters gene activity without changing the DNA sequence.
In labs: black coat (B) is dominant to brown coat (b) normal vision (N) is dominant to blindness (n) The genes for coat color and vision are on separate chromosomes. You cross a dog that is heterozygous for coat color and vision with a black blind dog. The black blind dog is heterozygous for coat color. What is the probability of getting a brown pup with normal vision?
BbNn x Bbnn FOIL each genotype for each parent BbNn= BN, Bn, bN, bn Bbnn= bn, Bn Proceed to use the Punnett square. 1/8.
In labs: black coat (B) is dominant to brown coat (b) normal vision (N) is dominant to blindness (n) The genes for coat color and vision are on separate chromosomes. You cross a dog that is heterozygous for coat color and vision with a black blind dog. The black blind dog is heterozygous for coat color. What is the probability of getting a brown pup with normal vision? *Alternative method*
BbNn x Bbnn Multiply the traits of each parent separately Bb x bb= BB, Bb, Bb, bb Nn x nn= Nn, nn 1/4 x 1/2 = 1/8 Same answer!
How is blood type an example of co-dominance?
Blood type A is dominant to O (A glycoprotein only). A= I^A Blood type B is dominant to O (B glycoprotein only). B= I^B Blood type AB, however, are co-dominant (A and B glycoproteins). O=i
What happens to the cells of a person with Cystic Fibrosis?
Both alleles on gene are mutant CTFR due to their genotype ff. This leads to dehydrated mucus infected with bacteria.
What is a genotype?
Combination of alleles in an individual.
What is the heterozygote phenotype of co-dominance?
Distinct phenotypes of both parents.
What trait is seen in the first filial (F1) generation?
Dominant trait
Why was the pea used as a model organism?
Easy-to-see traits Controlled matings Many offspring Short generation time (only takes a few month)
What is a phenotype?
Expression of a trait.
What occurs during x-inactivation? does x-inactivation cause? When does it occur? What happens during subsequent mitotic divisions?
Extreme DNA packaging. One random X chromosome in each cell becomes condensed and therefore inactive. It occurs in early development. During subsequent mitotic divisions, the same X will be inactivated.
What is Mendel's law of segregation?
Genes come in pairs that segregate from one another in the formation of gametes. Segregation reflects the separation of homologous chromosomes during anaphase I of meiosis.
What are sex linked genes?
Genes that are on sex chromosomes.
Phenotype is determined by...
Genotype
What is phenotype determined by?
Genotype
Red-green colorblindness is caused by a sex-linked recessive allele. A color blind man marries a woman with normal vision whose father was color blind. What is the probability that they will have a color blind daughter? What is the probability that any daughter would be colorblind? (the way this question is worded - ONLY asking about daughters)
Genotype for colorblind man: X^cY Genotype for woman's father: X^cY Genotype for woman: X^cX Use a punnet square to cross X^cY with X^cX = XX^c, XY, X^cX^c, X^cY =1/4 =1/2
In Guinea pigs, black hair (B) is dominant over white (b), rough coat texture (R) is dominant over smooth (r), and short hair (S) is dominant over long hair (s). If a guinea pig heterozygous for all traits mated with a guinea pig that had white smooth long hair, what is the probability they would have a guinea piglet that is true breeding for white rough long hair? Assume the genes for hair color, hair texture, and hair length are on separate chromosomes.
Genotype of pig heterozygous for all traits: BbRrSs Genotype of pig w/ white smooth long hair: bbrrss Genotype of pig true breeding for white rough long hair: bbRRss Multiply the traits of each category separately Hair color cross: Bb x bb = Bb, Bb, bb, bb bb=1/2 Hair texture cross: Rr x rr = Rr, Rr, rr, rr RR=0 Hair length cross: Ss x ss = Ss, Ss, ss, ss ss=0 1/2 x 0 x 1/2= 0 percent chance
What happens if the gene for the coagulation factor is mutated?
Hemophilia (blood clotting disease) develops
What are alleles?
Hereditary factors resulting in contrasting traits.
Does the inheritance of one trait influence the inheritance of another trait?
If genes are on different chromosomes, do not affect each other.
Cystic Fibrosis is inherited as an autosomal recessive trait in humans. Two individuals, one who has cystic fibrosis and the other is a carrier (heterozygous), have children. What is the likelihood they will have a child who has CF? What is the likelihood that they will have three children who all have CF?
Individual 1: ff Individual: Ff Cross Ff with ff 50% Child 1: 1/2*Child 2: 1/2*Child 3: 1/2= 1/8 chance.
What is the product of a monohybrid cross?
Inheritance of one trait
What is the heterozygote phenotype of incomplete dominance?
Intermediate.
What is a dihybrid cross used for?
It follows the inheritance of 2 traits
What happens if the gene for dystrophin (muscular structure protein) is mutated?
It leads to muscular dystrophy
What are the characteristics of the Y chromosome?
Known as genetic wasteland Hemizygous Contain SRY gene
What is euchromatin?
Loosely packed DNA (acetyl groups attached) in which genes are easily expressed.
What are the characteristics of the X chromosome?
Lots of genes
What are the recombinant results of a dihybrid cross?
New traits that were not seen in the parents that are now seen in the offspring.
Are both parents affected in autosomal dominant?
No; usually only one parent is affected
What does autosomal dominant mean?
Only one mutated allele needed *Only some abnormal protein is needed to have the trait*
What is the genotype of a dominant homozygous trait?
PP
In incomplete dominance, genotypic ratio equals...
Phenotypic ratio.
What is the genotype of a heterozygous trait?
Pp
Princess buttercup, a mother with type A blood, has a child with type O blood. Prince Humperdinck, who has type AB blood, claims he is the father. Can Prince Humperdinck be the father?
Princess buttercup genotype: AO Prince Humperdinck genotype: AB When crossed using a punnett square, there is no possibility for offspring with O blood.
What is independent assortment?
Random alignment of chromosomes on the metaphase 1 plate.
What trait is hidden in the first filial (F1) generation?
Recessive trait
How can you recognize a sex-linked recessive trait in a pedigree?
Recessive: Individuals with condition have parents who do not have condition Sex-linked: Only (for mostly) one sex affected
How can you tell if a trait is dominant or recessive in a pedigree?
Recessive: not seen in parents but seen in offspring Dominant: seen in offspring and at least one parent
What happens if the gene for opsin (eye cone pigments) is mutated?
Red-green colorblindness occurs
What happens when an egg of a pea plant is fertilizing?
Seeds form.
What does hyper-methylated mean?
Silences gene.
Huntington's Disease (HD) is an incurable, fatal neurological disease. It is inherited in an autosomal dominant manner. Median age of diagnosis of HD is ~ 38 years. Peter is a 30-year old individual whose father had HD. Neither Peter's mother nor a much older sister, who is 48 years old, show any signs of Huntington's. What is the probability that Peter has inherited HD?
Sister's genotype: hh Father's genotype: Hh Mother's genotype: hh Cross Hh with hh to find the answer 50%
What does hemizygous mean?
The gene can't be heterozygous or homozygous.
What is the F2 generation?
The offspring of the first filial (F1) generation. Trait hidden in F1 comes back out in F2.
What is the first filial (F1) generation?
The offspring of the parental generation.
What is the P generation?
The parental generation. True-breeding plants.
What is the SRY gene?
The testes determining factor, sets male development in embryo into motion.
What do Acetyl groups do to histones?
They attach to the tails of the histones which loosens the histone cluster, creating a 30nm fiber.
What is heterochromatin?
Tightly packed DNA in which genes are unable to be expressed.
What is blending inheritance?
Traits from two parents produces offspring with characteristics that are intermediate between those of the parents. This theory was discredited.
What are the parental results of a dihybrid cross?
Traits that were seen in the parents that are now seen in the offspring.
What does de-methylation mean?
Turns gene back on.
What is incomplete dominance?
When one allele does not completely dominate another allele, and therefore results in a new phenotype.
When can the dependent assortment method be used?
When the two genes are on the same chromosome.
How does a dihybrid cross of two traits on different chromosomes work?
You can FOIL the two genotypes of the different traits. Then proceed to use the Punnett square.
What is the genotype of a recessive homozygous trait?
pp
