BIO 260 - Genetics Exam 1 Material

What are the characteristics that make an organism ideal for genetic studies?

1. Short generation time (short life cycle)

2. Production of numerous progeny (able to produce lots of babies for quantifiable results)

3. The ability to carry out controlled genetic crosses (you want to know the genetics that you’re working with)

4. The ability to be reared in a laboratory environment (low maintenance organism, low contamination risk)

5. The availability of numerous genetic variants (Availability of many known mutants and natural variants for comparison)

6. An accumulated body of knowledge about their genetic systems (lots of genetic data that is open)

What are the major divisions of genetics

Transmission Genetics

Molecular Genetics

Population Genetics

Transmission Genetics (Mendelian/classical)

Examines principles of heredity

Molecular Genetics

deals with processes underlying gene expression

Population Genetics

studies genetic composition of groups of organisms

Who is the father of modern genetics and why are they considered that?

Gregor Mendel

He was not the first to think about inheritance, but he was the first to carry out quantifiable experiments and apply the scientific method to the question “how are traits passed down?”

The principle of segregation came from Mendel’s ______ 

Independent assortment came from Mendel’s ______

monohybrid crosses 

dihybrid crosses

Gregor Mendel Findings:

Deduced fundamental laws of genetics using garden peas

Parents pass on ‘heritable factors’ (genes) to their offspring responsible for inherited traits

Dominant and Recessive labels

Why did Mendel’s Experiments work so well

Controlled his matings

Pea plant was a model organism

Studied 7 characteristics that occurred in two forms, making him get clear numbers (either one or the other)

Characteristic

Feature you can measure or describe (e.g. color of flower)

Gene

An inherited factor that helps determine a characteristic

Allele

A version of a gene

Locus

The specific place on a chromosome occupied by an allele

Genotype

Set of alleles in an individual

Phenotype

Set of traits in an individual

Heterozygote

Individual with two different alleles at a specific locus

Homozygote

Individual with two identical alleles at a specific locus

Homologous Chromosomes

Pairs of matching chromosomes in diploid organisms, with one inherited from each parent

1. Homologous Chromosomes

2. Gene Loci

3. Dominant Allele

4. Recessive Allele

5. PP - homozygous for dominant allele, aa - homozygous for recessive allele, Bb - heterozygous

What question did Mendel want to answer?

if offspring of parents with distinct traits display either of the parental phenotypes or a blended phenotype

Monohybrid Crosses

1. A cross between two true-breeding parents that differ for one characteristic

2. 3 generations (P, F1, F2)

3. 2 crosses (PxP, F1xF1)

True Breeding

Parents are homozygous for specific traits, leading to offspring that do not show trait variation across generations

Intercross

Genotypes of the parents are different (RR x rr)

P Generation

These are the true-breeding parents used for the initial cross (RR x rr)

F1 Generation

The first set of offspring from the P generation cross. These are typically hybrids (heterozygous) and show only the dominant trait

F2 Generation

Offspring produced by the self-pollination or crossing of two individuals from the F1 generations (siblings omg)

What do you do to get to an F2 Generation when given parents genes?

Cross Parents to get F1 generation, cross F1 to get F2

What did Mendel Conclude?

The traits of the parents do not blend

F1 must have information from both parents, it is the only way in which both traits can re-emerge in the F2

Concept of Dominance - one version of a gene can mask a different version of the same gene

Individuals must carry two copies of each ‘factor’ which separate with equal probability when gametes are formed to explain the 3:1 in F2

Principle of Segregation

Diploid organisms possess two alleles for any particular trait, which separate (segregate) during meiosis, ensuring each gamete carries only one allele for each gene

Backcross

Take an F1 and cross it with one of the parents to produce offspring with genetic characteristics closer to that parent

Self Cross

Crossing two F1s, crossing it with the same genotype basically (Rr x Rr)

Genotypic Ratio

Look at all possible genotypes (1 RR:2Rr :1 rr)

Phenotypic Ratio

Look at all possible phenotypes (3 round:1 wrinkled)

Test Cross

used to determine if an individual with a dominant phenotype (and unknown genotype) is homozygous dominant or heterozygous

Reciprocal Cross

Switch the phenotypes of the parents to determine if the inheritance pattern is influenced by the parent's gender

• so if in the first cross the female phenotype is PP, the reciprocal cross will be pp (same for male)

What cross would you set up if you want to find out the genotype of an organism displaying a dominant phenotype?

test-cross

The Multiplication Rule

The probability of two or more independent events occurring together is calculated by multiplying their independent probabilities

Language to look out for in questions: “and“

Independent Event

when the outcome of one event does not affect the probability of another

The Addition Rule

The probability of any one of two or more mutually exclusive event is calculated by adding the probabilities of these events

language to look out for: “or“

Mutually exclusive events

events that can’t happen at the same time

Probability

Odds/chances something will happen

expressed as a value from 0-1, with 0 meaning it is impossible and 1 meaning it is certain

n = # trials

s = number in one class

t = number of other class

p = probability of outcome s

q = probability of outcome t

Dihybrid Crosses

Analyzing the inheritance patterns of two distinct genes simultaneously (RRYY x rryy)

Law of independent Assortment

Alleles at different loci separate independently of one another 

When does the law of independent assortment occurr

During meiosis I, metaphase I when homologous chromosomes line up RANDOMLY

The Law of independent Assortment was derived by Mendel’s ____

Dihybrid Crosses

Dihybrid Crosses give you ____ combinations

16

Observing a phenotypic ratio of 9:3:3:1 is indicative of what type of cross?

Double heterozygote x double heterozygote

When given a dihybrid problem, use a ___

branch diagram

Mendel’s principles of inheritance

Law of segregation (1st law)

Law of independent assortment (2nd law)

Genetics

The science of heredity, dealing with resemblances and differences of related organisms resulting from the interaction of their genes and the environment

Branch Diagrams

Used to determine the phenotypic ratio of a dihybrid cross

Observing a phenotypic ratio of 1:1:1:1 is indicative of what type of cross?

double heterozygous x double homozygous for recessive allele

The Goodness of fit Chi-Square Test

A test that measures how a hypothesis/model compares to actual data

Indicates the probability that the observed deviation is due to chance

P < 0.05 (5%)

reject the null

P > 0.05 (5%)

fail to reject the null

Duplicated Chromosomes

Consist of two sister chromatids

Homologous Pair

Consist of two chromosomes, a maternal and a paternal

Diploid cells (2n)

Carry two sets of genetic information (pairs of homologous chromosomes/allele pairs)

Haploid cells (n)

Carry one set of genetic information (one chromosome/one allele from the pair)

We have 22 ___ and one pair of___

autosomes

sex chromosomes

Karyotype

An arrangement of chromosomes, allow to see chromosomes (usually done during pregnancy to see if something needs investigating) 

Trisomy 21

extra copy of chromosome 21 (three instead of 2) resulting in down syndrome and other symptoms

1. Telomere

2. Centromere

3. Sister chromatids

4. telomere

5. kinetochore

6. spindle microtubules

Centromere

DNA region on chromosome area where kinetochores assemble and allow attachment of spindle microtubules

When counting chromosomes, count the __

centromeres

Telomeres

Tips of a linear chromosome, protect from genetic data loss and deterioration during cell division (they shorten every time, once too short, they go through cell death)

Chromosomes are made up of ___

chromatin

Chromatin

DNA wrapped around histone proteins

What does the wrapping of histones allow?

It allows huge amounts of DNA to fit into a very small space (nucleous)

1. Chromatin

2. DNA

3. Histone Proteins

Meiosis

The first part of sexual reproduction, the second is fertilization

one of two types of cell division (mitosis)

Meiosis produces genetic _______

variation in sexually reproducing animals

A cell that’s gonna divide by meiosis will go through ___

interphase

Interphase (S-Phase)

Chromosomes and DNA duplicates

Meiosis I gives you _____

2 Haploid cells

Meiosis II gives you ____

4 Haploid cells

To count number of chromosomes in meiosis, count the ___

centromeres

Amount of DNA refers to the amount of ___

chromatids

Crossing over occurs in ___

Prophase I

Meiosis Consists of

Interphase (S-Phase)

Prophase I

Metaphase I

Anaphase I

Telophase I

Prophase II

Metaphase II

Anaphase II

Telophase II

What are the sources of genetic variation that occur in meiosis, and in what phase do they occur

Crossing over, happens in prophase I

Random alignment of homologs, happens in metaphase I

2^n calculates what

The number of possible gametes arising from independent assortment alone 

where n is the number of homologous pairs in cell

Sex

refers to sexual phenotype. Most organisms have two sexual phenotypes, male & female, in which one of the fundamental differences is the size of their gametes

Male gametes contribute

nuclear DNA

which gamete is bigger, male or female?

female #swag

XX Male Syndrome

human with genotype XX (with translocated SRY gene), displaying male anatomy, is referred to as being male

sterile male

Androgen Insensitivity Syndrome

XY individual develops female phenotype, but no uterus + underdeveloped gonads (no testosterone receptor expressed)

SRY is what and where is it located

Sex determining region Y-protein

very top of the Y chromosome

Swyer Syndrome

Mutation in SRY that results in a phenotypic female

What are the main Sex-Deterrmining Mechanisms

Genic

Environmental

Chromosomal

Genic Sex Determination

Genetically determined but there are no sex chromosomes, sex is controlled by genes

No chromosomes that stand out as sex chromosomes

what are some organisms that follow genic sex determination

some plants, fungi, protozoans, and fishes

Environmental Sex Determination

Sex is determined fully or in part by environmental factors

what are some organisms that environmental sex determination

turtles - lower temp gives you male, high temp gives you female

limpet - first larva that attaches to a rock is a female, then others that attach is male

Chromosomal Sex-Determining Systems

utilize sex chromosomes to determine an organism's biological sex

what are the three chromosomal systems

1. XX-XO

2. XX-XY

3. ZZ-ZW

Heterogametic

organism that consists of sex chromosomes that differ

Homogametic

organism that consists of the same sex chromosomes

XX-XO: males are _____, females
____

heterogametic

homogametic