Chapter 9: Genetics
What is an allele?
Any of the different forms of a particular gene
How do different alleles of the same gene arise?
They arise from mutations: Any change in the DNA that make up a gene ----- the allele's instructions will then result in a protein that differs from the original version
The gene for hair texture exhibits three phenotypes, straight, wavy, and curly. A man and a woman, who both have wavy hair, have children. What fraction of the children would you expect to have straight hair?
1/4 If HS = straight and HC = curly,then the cross performed here would be HSHC × HSHC and the Punnett square would look like this: HS HC HS HSHS HSHC HC HSHC HCHC Only individuals with the genotype HSHS would have straight hair.
Purebread animal are homozygous for all or nearly all of the accepted breading standard for that breed. They will produce pups that have the distinctive qualities of that particular breed. How about a mutt?
A mutt will be heterozygous for many phenotypes.
What is homozygous? What is heterozygous?
An individual that has two copies of the same allele: WW or ss An individual with a genotype of two different alleles: Ss
Dihybrids cross
Breeding individuals that are heterozygous for two different traits. (9:3:3:1) was the ration Mendel discovered. It shows that traits are inherited separately from one another. Genes from traits are inherited independently from one another.
The allele that is visible in the phenotype of a heterozygous individual is known as the _________ allele because it masks the other allele that must be present in that individual.
Dominant
True or False? A Punnett square tells us with absolute certainty what the outcome of a genetic cross will be.
False Probability is only a measure of the chance that we will see a particular result.
True or False? A gene has four alleles. A diploid individual would carry eight alleles for that gene in its DNA.
False A diploid individual can only have two alleles for any gene. One allele is inherited from each of the individual's parents.
What are all the possible gamete genotypes produced by a Pp purple pea flower?
P Big P or p Little p
albinism
Pleiotropy is at work here. A single gene influence eye color and hair and skin = albino most common type of albinism involved the melanin production ---- eyes produce melanin, also skin obviously
What are all the possible gamete genotypes produced by this plant that produces smooth, yellow seeds? RrYy
Remember that a gamete has one copy of every gene. That means we should see one "R" and one "Y" in every possible answer. RY Ry ry rY
Are somatic cells in plant and animals haploid or diploid?What does this mean?
The are diploid (2n). They carry two copies of each type o chromosome
Phenotype
The display of a particular version of a genetic trait. -fawn, sable, apricot coat in a dog
Some genetic traits are INVARIANT. What does this mean?
The trait is the same (or nearly the same) in all individuals of a population. -i.e we all have two eyes
How is diversity expressed in a population?
There will be different alleles for different genes.
pleiotropy Pleiotropic gene
When a single gene influences a variety of different traits A gene that can influence two or more distinctly different traits.`
What does the law of independent assortment do?
When gametes form, the alleles of a particular gene segregate during meiosis independently of the other genes.
Epistasis
When to phenotypic effect of the alleles of one gene depends on the presence of certain alleles for another, independently inherited gene.
incomplete dominance vs Co dominance
With incomplete dominance pink is possible from blue and red flowers With co dominance, both traits with be be expressed at the same time
Genetic trait
an inherited characteristic of an organism that can be detected or observed. -Genetic traits are controlled by genes, but also by the environment -Physical traits = height, shape of face -Biochemical traits = hair color, skin color
The situation in which one gene impacts two or more distinct phenotypes is known as ________ .
pleiotropy
A man with type B blood and a woman with type A blood have several children. At least one child has type O blood. What are the genotypes of the man and the woman?
woman IAi man IBi
Summarize Mendel's' concepts
1. Alternative versions of genes cause variation in inherited traits 2. Offspring inherit one copy of a gene from each parent 3. An allele is dominant if it has exclusive control over the phenotype of an individual when paired with a different allele. 4. Two copies (alleles) of a gene segregate during meiosis and end up in different gametes 5. Gametes fuse without regard to the alleles they care.
1. Law of segregation 2. Law of independent assortment
1.Law of segregation: The two copies of a gene are separated during meiosis and end up in different gametes 2. When gametes form, the alleles of a particular gene segregate during meiosis independently of the alleles of other genes.
What is the minimum number of genes the inheritance of which you must be following for the law of independent assortment to apply?
2 Independent assortment only applies when you are following the inheritance of more than one gene.
What is a gene?
A gene is a segment of DNA on a chromosome that describes how to make a certain protein. - Genes are located at a specific locus on the chromosome
Homologous Pair
A pari of chromosomes, one from the father and one from the mother. - Paternal homologue -Maternal homologue
Punnett square
A punnett square shows all the different ways two alleles can be brought together. It lists all the possible genotypes.
Which of the following is a statement of Mendel's law of segregation? 1The order in which the two copies of one gene are separated is not affected by the order in which the two copies of another gene are separated during gamete formation. 2. Every sperm has an equal chance of fertilizing an egg. 3. In a heterozygous individual, one allele always masks the other allele. 4.The two copies of a gene in a diploid individual are separated during gamete formation.
#4
Concept check: 1. What is an allele? How do new alleles arise? How many different alleles can a person cary for a particular gene? 2. For a single genetic trait, what is the difference between a genotype and a phenotype?
1.An allele is a form of a particular gene. New alleles arise through mutation. A person can have two different alleles of a gene. 2. The genotypes is the letters (Ww or WW) and the phenotype is the actual physical expression of the genotype.
Homozygous vs Heterozygous
BB Two copies of the same allele Bb Two different copies of the same allele
True or false? All genes and alleles follow Mendel's laws of inheritance.
False Although the law of segregation is universal, other aspects of Mendel's laws vary between genes.
DNA is made up of ACT and Gs
The gene resides at a particular locus on a gene. Different alleles result in different expression of a gene ---- Blue eyes /Brown eyes The genes are always located in the same place on the chromosome, but the form may be different (B b A a, etc.
Mutations occur at random, with not specific purpose. True or false?
True In multicellular organisms, only mutations that are present in the gametes can be passed to offspring.
The laws of segregation
Two copies of a gene are separated during meiosis and end up in different gametes
