Bio Unit 10

Genetics

What is the difference between genes and alleles

-a gene is a part of the DNA. Alleles refer to different versions of the same gene

What is an example of gene vs allele?

Gene: Hair type

Allele: Curly

What is Heredity

Transmission of traits from 1 generation to next

What is Genetics

Study of how traits pass from parents to offspring (heredity)

Which cells responsible for passing traits on?

Gametes

Which type of cell division makes these cells?

Meiosis

Purpose of this cell division

Reduce chromosome \# by half & genetic variation

Which specific part of the cell carries the trait?

Chromosomes/ genes

What is this specific part made of?

DNA

What are Mendel's Laws?

trait are determined by genes, an adult has 2 versions of each gene, law of dominance, law of segregation, law of independent assortment

What is Mendelian Genetics

a theory of genetic inheritance which was developed by Gregor Mendel

What experiment helped mendel make these laws

Mendel experimented with pea plants in order to find out the laws.

Why did Mendel use pea plants?

7 traits each with 2 contrasting alleles, Short generation times, Produce large # offspring, Can control matings, Self vs Cross-pollination

What is mendel's law, about traits, about

Traits determined by genes ("heritable factors") & there are alternative versions of each gene = alleles & they are passed on via chromosomes in gametes.

•Genes are located on chromosomes

How many copies does an organism have of a gene?

Every organism has two copies of every gene

What is mendel's law, about genes, about

Most sexually reproducing adults have 2 versions of each gene (AKA 2 alleles) one from each parent

Why does each individual have 2 alleles for each trait?

because it's from two parents

What are the exceptions to mendel's law, about gene

multiple alleles and polygenic traits

What are multiple alleles

ONE gene has \>2 alleles as variations for that trait (as opposed to only 2 alleles; dom and rec. This leads to having \>3 genotypes and phenotypes

what are multiple alleles for dummies

three or more forms of a gene that code for a single trait

What is an example of multiple alleles

Blood typing gene has 3 possible alleles: A, B, O

6 possible genotypes: AA, AO, BB, BO, AB, OO

4 possible phenotypes:Type A, Type B, Type AB,Type O

What are polygenic traits?

ONE trait is determined by \>1 gene on different chromosomes. Again this can lead to a much greater \# of genotypes and phenotypes than 2 or multiple alleles because the genotypes and phenotypes are made up of 3 or more genes each with 2 alleles.

What is a polygenic trait for dummies

trait controlled by three or more genes

What is an example of a polygenic trait

Skin color (determined by 3 separate genes) leads to a large variety of skin tones from white to tan to black

Hair Color, Eye Color, height, etc.

What is the Law of Dominance

Dominant allele masks recessive allele when the organism has both alleles

what experimental results helped Mendel concluding the law of dominance

When mendel was doing his experiment with pea pods, when f1 came up, it masked and made all the pea plants tall

What are exceptions to the law of dominance

incomplete dominance and codominance

What is incomplete dominance?

The dominant allele does not fully mask the recessive allele when both are present leading to a blended phenotype between dominant and recessive phenotypes leading to a 3rd possible phenotype

What is incomplete dominance and an example for dummies

A blending of traits. Red+White\=Pink.

What is an example of incomplete dominance

Red snapdragons (RR) crossed with white snapdragons (rr or R'R') leads to pink (Rr or RR') snapdragons

Humans and hypercholesterolemia- HH= normal # receptors for LDL, Hh= minimal amount of receptors for LDL, hh= no receptors for LDL greatly increasing risk for plaque formation and heart attacks.

FYI: genotypic ratios will be the same, but phenotypic ratios will differ

ex) Rr x Rr is 1RR: 2Rr: 1 rr genotypes just like in complete dom, but phenotypic ratio is 1 red: 2 pink: 1 white unlike complete dominance which is 3 red: 1 white

What is codominance

Both alleles are dominant so both get expressed and can be seen in the phenotype separately not blended leading to a 3rd possible phenotype.

What is codominance for dummies?

when both alleles contribute to the phenotype and are both present

What is an example of codominance

Black guinea pigs (BB) crossed with white guinea pigs (WW) result in black & white speckled (agouti) guinea pigs

A & B alleles in blood typing are codominant to each other

FYI: genotypic ratios will be the same, but phenotypic ratios will differ

ex) RW x RW is 1RR: 2RW: 1 WW genotypes just like in complete dom, but phenotypic ratio is 1 red: 2 red & white speckled: 1 white unlike complete dominance which is 3 red: 1 white

Does codominance and incomplete dominance effect the genotype

no, just the phenotype

What is the law of segregation?

Alleles separate during gamete formation (meiosis)

AKA Homologous chromosomes separate

What is the Law of Segregation for dummies

two copies of genes(AKA HOMOLOGOUS CHROMOSOMES) must separate during gamete production

What helped Mendel explain the law of segregation

observing that pea plants with two different traits produced offspring that all expressed the dominant trait, but the following generation expressed the dominant and recessive traits

What is the law of independent assortment?

Alleles on different homologous chromosomes line up & separate independently of each other during meiosis metaphase I

Traits DO NOT influence each other

Explains dihybrid cross and ability to use probabilities to calculate possible offspring

What is the law of independent assortment for dummies

Genes for different traits are inherited independently of each other

What are the exceptions to the law of independent assortment

linked genes and sex linked genes

What are linked genes

2 genes are unable to independently assort from each other because they are located on the same chromosome so the only way to get alternative gametes and fertilizations (ex- TR and tr vs. Tr and tR) is if crossing over randomly happens during gamete formation.

What are linked genes for dummies

genes located on the same chromosome that tend to be inherited together

what is an example of a linked gene

Gray body color and normal wing size in fruit flies are on the same chromosome

There are many genes on the same chromosome and the distance between genes determines how often crossing over happens. For example, if 2 genes are far apart, then there is greater chance for crossing over than if the 2 genes are closer together.

What are sex-linked genes?

Genes that are specifically on the sex chromosome (typically, but not exclusively on the X-chromosome). This means that the gene is inherited with gender (AKA linked to gender or sex). Otherwise genes that are located on the autosomes are called autosomal traits and are not linked with gender

What are sex linked genes for dummies

Genes located on the sex chromosomes.

what is an example of a sex linked gene

In humans, color blindness, hemophilia are sex-linked recessive diseases

What is a linked gene

genes on the same chromosome

How results of a cross that is with linked genes causes dependent assortment compared with genes that are on separate chromosomes allowing independent assortment

The genes are linked, so they travel together as a pair. When crossing over happens it allows for variations (rare)

What is a important fun fact about crossing over

Crossing over occurs with more frequency when genes are farther apart on the same chromosome vs when closer together

Recombinants

individuals with new combinations of genes, result of crossing over

What is a genotype?

genetic makeup of an organism

What is a phenotype?

physical characteristics of an organism

What is a locus

Location of a gene on a chromosome

a sentence that demonstrates the relationship between homologous chromosomes, genes, traits, and alleles

Alleles are the specific traits of a gene, which is in homologous chromosomes.

What is a genotype? Why does each cell have 2 alleles for every genotype?

A genotype is the genetic makeup and a cell has 2 alleles for every genotype because there are two parents.

What is a phenotype and how do alleles determine the phenotype?

A phenotype is the physical characteristics being read from a genotype. The alleles determine the phenotype because alleles determine the specific characteristics.

How many traits is a monohybrid cross crossing?

1 trait from each parent, and basically just crossing two gamates

How many traits is a dihybrid cross crossing?

2 traits from each parents

What is a test cross

a mating between an individual of unknown genotype and a homozygous recessive individual to test if it's homozygous or heterozygous dom

What is a monohybrid cross

A cross between two individuals, concentrating on only one definable trait

What is a dihybrid cross

Cross or mating between organisms involving two pairs of contrasting traits

What is the FOIL method?

First, Outer, Inner, Last

How can the foil method be used for dihybrid crosses?

To find what to cross for a dihybrid cross

What experiment helped mendel conclude about the law of independent assortment

the pea's traits were recessive again so mendel concluded they did it independently

incomplete dominance

A pattern of inheritance in which two alleles, inherited from the parents, are neither dominant nor recessive. The resulting offspring have a phenotype that is a blending of the parental traits.

complete dominance

The situation in which the phenotypes of the heterozygote and dominant homozygote are indistinguishable.

incomplete vs codominance

In incomplete dominance heterozygous individuals have a blend of the two parental phenotypes (RW\=Pink). In codominance, heterozygous individuals show both phenotypes individually in the form of stripes, spots, or speckles (RW\=Red and White).

Codominance

A condition in which both alleles for a gene are fully expressed

What are sex-linked traits?

Genes that are located on the sex chromosomes (x) that are not related to sex determination.

Ex: color blindness and hemophilia

What is hemophilia?

A disorder in which blood doesn't clot normally

What is an antigen

a toxin or other foreign substance that induces an immune response in the body, especially the production of antibodies.

what is an antibody

a blood protein produced in response to and counteracting a specific antigen

What is a multiple allele trait

A trait that has more than three alleles. Example: there are three alleles for human blood types.

What is a polygenic trait?

trait controlled by two or more genes

Multiple Allele trait vs polygenic trait

The difference is genes vs alleles

What is a trait

A characteristic that an organism can pass on to its offspring through its genes.

What is a gene

A segment of DNA on a chromosome that codes for a specific trait

What is an allele

Different forms of a gene

What are homologous chromosomes

Chromosomes that have the same sequence of genes and the same structure

What are the generations of heredity?

Parent generation\= P-gen, 1st Filial generation\= F1 gen, 2nd filial generation\= F2

what is P-gen

parent generation

what is F1 gen

1st Filial generation

What is F2 gen

offspring of F1, 2nd filial gen

what is the difference between Homozygous and Heterozygous

Homozygous is two of the same letters, whether uppercase or lowercase, while heterozygous is half and half (opposites)

What is heterozygous?

Organisms have two different alleles for a particular trait.

Another name for heterozygous

hybrid

What is homozygous?

organisms that have two identical alleles for a particular trait

Another name for homozygous

purebred

what are antigens

a toxin or other foreign substance that induces an immune response in the body, especially the production of antibodies.

What does type b blood produce

anti-A antibodies and b antigens

What does type A blood produce

anti-B antibodies and a antigens

What does type ab blood produce

no antibodies, universal acceptor of RBCs

What does type o blood produce

anti-A and anti-B antibodies

what is this pedigree

dominant autosomal

What is recombination?

the rearrangement of genetic material, especially by crossing over in chromosomes or by the artificial joining of segments of DNA from different organisms.

What can linked genes show?

recombinants

What makes a pedigree autosomal dominant?

Need just one copy of the mutant allele. Affected males and females have an equal probability of passing on the trait to offspring.

What makes a pedigree autosomal recessive?

Need two copies of the mutant allele. When have one copy of mutant allele, an individual is a CARRIER of the mutation, but is normal. Can have female & male carriers. Females and males are affected equally

What makes a pedigree dominant sex linked?

ALL daughters of an affected male will be affected. Females and males are affected equally

Because the gene is located on the X chromosome, no father son transmission, but there is father daughter

Children of an affected woman have a 50% chance of inheriting the X chromosome with the mutant allele.

What makes a recessive sex-linked?

Need 2 copies of mutant alleles. Males affected more than females. Because the gene is on the X chromosome there is no father son transmission.