Heredity/Genetics

diploid

2 full sets/pairs of chromosomes within a cell; represented by 2n

• created by 2 haploid gamete cells

haploid

1 set of chromosomes within a cell; represented by n

gamete

a reproductive cell of an animal or plant

Crossing Over

• occurs in Prophase I of Meiosis I

• nonsister chromatids of double homologous chromosomes exchange segments

• results in recombinant chromatids

  • increases genetic diversity

homologous

having similar or corresponding features

fertilization

• one gamete from each parent fuse together to form a diploid offspring

• is random

  • increases genetic diversity

Features of genetic code shared by modern living systems

1. all organisms use nucleic acids to store + transmit genetic info.

2. all organisms have ribosomes + use them to synthesize proteins

3. all organisms perform Cellular Respiration; Glycolysis is a conserved aspect of it

gene

a unit of heredity coding for a trait; can be transferred from one generation to the next

trait

a genetically determined characteristic of an organism; genes determine these

allele

a specific variation of a gene(a unit of heredity coding for a characteristic of an organism)

• inherited from both parents

• organisms inherit different version for the same gene

• represented w/ letters

dominant allele

always shows in phenotype if inherited

recessive allele

only shows in phenotype when dominant allele has NOT been inherited

genotype

the combination of inherited alleles; represented by 2 letters

homozygous

the combination of inherited alleles(genotype) containing 2 of the SAME alleles

heterozygous

the combination of inherited alleles(genotype) containing 2 DIFFERENT alleles

phenotype

the PHYSICAL RESULT or expression of the genotype

Law of Segregation

1. chromosomes carry alleles(specific variations of units of heredity that code for characteristics)

2. homologous chromosomes carry alleles(specific variations of units of heredity that code for characteristics)

3. when chromosomes are separated into daughter cells during Meiosis, alleles for each trait are separated

4. separation of alleles allows for genetic variation

5. reappearance of recessive pheonotype in F2 generation is evidence of segregation of alleles

Law of Independent Assortment

1. 2 or more genes(units of heredity for characteristics) assort independently of each other

2. one trait(characteristic) is not automatically inherited w/ another trait(characteristic)

3. alleles for separate traits can be packages in every possible combination into gametes(sex cells)

Determining Probability of A OR B happening

add the probability of A to the probability of B

Determining Probability of A AND B happening

multiply the probability of A to the probability of B

monohybrid cross

an examination of how one trait is inherited

dihybrid cross

an examination of how two traits are inherited

pedigree

a visual representation tracing the history of a trait through familial generations

• circles = biological females

• squares = biological males

• generations indicated w/ roman numerals

• those affected by a trait are shaded in

autosomal dominant traits

traits that show a pattern of affected offspring with affected parents

autosomal recessive traits

traits that show a pattern of affected offspring with unaffected parents

Hypothesis Testing

used by scientists to reject or fail-to-reject statistical hypothesis; helps to determine if there is a difference in numerical data due to the what they’re testing(independent variable) or chance

Null Hypothesis

states there is NO RELATIONSHIP or NO DIFFERENCE between two groups of data in an investigation

Alternative Hypothesis

one of MANY possible hypotheses that states observed results are due to a NONRANDOM cause; there IS A RELATIONSHIP between two groups in an investigation

Chi-square goodness-of-fit test

used to determine if there is a significant relationship between 2 groups of data

• observed outcomes are compared to expected outcomes to see if variations could be due to chance

• often used to test genetic crosses

Steps to perform a Chi-square goodness-of-fit test

1. establish research question

2. determine null hypothesis

3. determine alternative hypotheses

4. count observed values

5. determine expected values

6. calculate chi-square value

7. calculate degrees of freedom

8. select p value

9. identify critical value

10. compare chi-square value to critical value to draw conclusions

Chi-square values and Null Hypotheses

1. if chi-square value < critical value, FAIL TO REJECT null hypothesis

2. if chi-square value > critical value, REJECT null hypothesis

linked genes

genes that are adjacent and close to one another on the same chromosome and that are inherited together; less likely to be separated during crossing over in meiosis

sex-linked traits

traits that are determined by genes located on sex chromosomes

map distance

tells you how close together a pair of linked genes is; determined by how frequently a pair of genes participates in a single crossover event

recombination frequencies

a measure of the likelihood that two genes located on the same chromosome(linked genes) will be separated during meiosis through crossing over

• linked genes have this < 50%

• if linked genes have 5% of this, they are close together on the chromosome; considered 5 map units apart

• if linked genes have 30% of this, they are further apart on the chromosome; considered 30 map units apart

environmental factors on gene expression

environmental factors can influence gene expression; if environmental conditions change, expression of gene can change

ex: hydrangeas changing color based on soil acidity

phenotypic plasticity

the ability of one genotype to produce more than one phenotype; organisms can have same genes but show different forms based on external factors

Law of Segregation

separation of alleles during gamete formation:

1. each gamete carries only one allele for each gene therefore each gamete receives only one parental allele

2. segregation of parental alleles into gametes provides opportunity for more varied combinations of alleles when fertilization occurs

independeent assortment

suggests that genes for 2 or more traits will be sorted into gametes independently; genes are NOT linked

• inheritance of each gene is random/not connected to inheritance of any other gene

• provides more possible gene combinations when fertilization occurs

random fertilization

refers to concept that any of genetically unique sperm created by a male can join with any of the genetically unique eggs created by a female; produces offspring with a genetically unique combination of chromosomes

nondisjunction

the failure of chromosomes to fully separate during the formation of gametes; results in too many/to few chromosomes in sex cells