Heredity Slide 1-36

Based on Lecture Vid and Supplement

Chromosomes

• contain the genetic code - DNA

  • DNA are the blueprints that make up all the info necessary to create a human

  • includes all the protein formations necessary to allow you to exist

• occur as homologous pairs

  • these pairs code for characteristics like having long or short fingers

  • each parent gives one set of instructions to make you

Gregor’s Subjects

• used peas

• selected traits that bred true

  • flower color

  • seed shape

  • seed color

  • pod shape

• carried out crosses

• counted numbers of offspring expressing a trait

Trait

• some expressible characteristic of an organism: eye color, blood type, flower color

  • overall visible characteristic we look at and can also be chemical (by looking at proteins on surfaces)

Gene

• each trait is controlled by a gene

• a discreet section of DNA that codes for a functional protein or RNA molecule

• occur in pairs (one from mom, one from dad)

• unit of instruction for producing or influencing a specific trait; the genes have specific locations (locus, loci) on a pair of homologous chromosomes

Allele

• different molecular forms of a gene; an allele may be dominant (A) or recessive (a)

• all the molecular forms of a gene

  • different flavors of gene whether you get info about having blue or brown eyes represent the different types of alleles within that gene pairs

    • most genes have 2 forms of alleles

Dominant Allele

• the one expressed in a gene pair that contains different alleles

  • one expressed when there is a choice when the parents give two different alleles for a given characteristic

Homologous Chromosomes contain gene pairs that code for the same trait

• somewhere on the piece of DNA is a section that codes for a particular trait

  • ex. gene pair for flower color. One makes purple, one makes white.

Homozygous

• condition when both alleles contain the same information (either both recessive or both dominant (AA or aa)

  • when both parents gave exactly the same alleles

Heterozygous

• alleles present are different (one recessive and one dominant Aa)

Genotype

• the type of allele present in gene pair of the individual

Phenotype

• the physical characteristic expressed by the individual and is observable

  • what results from the genotype

Law of Segregation

• each gene pair is split during meiosis

• which gametes end up with which half of the gene pair is completely random

• each gamete must contain an allele from every gene pair

  • gametes are sex cells and have to contain one allele from each gene pair but not both

• diploid organisms inherit a pair of genes for each trait; meiosis segregates the two genes randomly

Punnett Square

• gives a probability table about what the results of this cross might be

Monohybrid Cross (P → F2 generation)

• F1 generation becomes a carrier of the recessive trait

  • crossing of 2 heterozygotes creates a 3:1 ratio

Law of Independent Assortment

• two traits on different chromosomes separate their alleles into gametes independently from each other

• only applies to genes on separate chromosomes

• each gene pair tends to sort independently of other gene pairs into gametes (so long as the gene pairs are on non-homologous chromosomes)

  • when they are on 2 different chromosomes there is nothing linking the separation of traits to the other chromosome and are thus independent of each other

Are the genes for seed color and shape on different chromosomes? Do they sort independently?

• is not perfect, uses statistics to see what the next generation is doing

Incomplete Dominance

• heterozygotic cells express either allele

• on cellular scale some cells are pigmented white and some red; resulting in pink flower (blends)

• phenotype of heterozygote is intermediate between either homozygous conditions ex. snap dragons

  • when there is a choice in the heterozygote, the cell picks one of the two alleles and is not true dominance

  • is basically flipping a coin over and over again

  • looks different under a microscope vs. the human eye

Co-Dominance

• not all genes have two alleles (AB blood expressed both A and B allele)

• expression of two different alleles simultaneously (blood groups)

• Blood has 3 Allleles: A, B and O

  • O is recessive and means you don’t make the protein

  • if you have A or B you have a dominant allele

  • when you have two dominant alleles, both are picked

  • can only happen to multiple alleles

Karyotyping: Chromosmes made visible

• takes WBCs because RBCs don’t contain DNA

  • these are then spun down and dyed to be looked at

Sex Determination

• determined by male in humans

• XY = male

• XX = female

• in diploid organisms most of the chromosomes are similar; but two homologous chromosomes are different in males compared to females - these are the sex chromosomes

  • does not apply to all other species

Autosomes

• chromosomes that are not XY

• code for traits in the body itself

X Inactivation

• when only one X is being expressed and the other is inactivated and folds up

• seen a lot in females due to being XX

• example. multicolored cats

Sex Linked Traits

• usually applies to X chromosome since the Y carries only a few genes; therefore since a male has only one X chromosome the genes on that chromosome are expressed whether they’re recessive or dominant

  • X are what we are most concerned about because it is bigger and contains more genetic info

  • are linked to a specific chromosome structure

    • ex. colorblindness and hemophilia

  • can still become a carrier

Gene Map

• physical location of a gene on a particular chromosome

• gene maps available for several organisms

  • humans, mice, fruit fly, C. elegans, monkey

Chromosome Variation

• 3 large changes on the chromosome itself

  • mutation

  • change in chromosome structure

  • chromosome change in number

Mutation

• a change in the DNA base sequence (ex. sickle cell anemia)

• any heritable change in the structure of DNA (may be bad, good, or neutral)

  • is substituting new DNA bases that change the amount of amnio acids, sequence of amino acids in a protein

  • happens on a irregular basis and are random

  • have capability to be inherited after they are there

  • cause problems eventually but live long enough to reproduce allowing it to continue in the populations to come and thus can’t be legal

Change in Chromosome Structure

• individual chromosomes change their structure through deletions, duplications, inversions, or translocation ex. Cri-du-Chat children (deletion of short arm of chromosome 5)

• rearrangement of the chromosome

  • big changes to the chromosome molecules

  • reversing the gene, upside down and move it to a different chromosome and will change the chromosomes function

Chromsome Change in Number

• caused by nondisjunction

• a cell may end up with one more or less than the correct number of chromosomes (aneuploidy) or may end up with three or more of each type of chromosome (polyploidy)

• occurs because of incorrect separation of chromosomes in mitosis or meiosis

Chromosome nondisjunction

• when one pair doesn’t split and results in either one having too many chromosomes or not having enough

Down’s Syndrome

• trisomy of chromosome 21, incidence varies with age of mother

• weak muscle tone, small mouth, distinct eyelid shape, low resistance to disease, heart malformations, mental retardation

  • extra chromosome

Klinefelter’s syndrome

• 1/1000 males; show at puberty, small testes, broader hips, and partial breast development

• sterile but generally not impotent, some mental deficiency present

  • too many X chromosomes and results in malformations of sexual development especially sexual maturity wise

Super Male

• 1/1000 males

• higher incidence of below average intelligence and above average height

  • extra Y chromosome

Turner Syndrome

• 1/1500 females

• sterile, short, lack 2 degree sex characteristics, and a web neck

• XO

  • receive an X chromosome, but don’t get a Y or a matching X chromosome

  • can’t generate normal eggs

Sex Influenced Traits

• trait expressed differently in the two sexes

• ex. baldness - reverses dominance pattern between male and female

• not X linked

• presence of sex hormones may intensify or alleviate degree of expression

  • is an autosomal trait but influenced on whether you make testosterone or not

Environment Influenced Genes

• properties of environment determine how gene is expressed

• ex. pH of soil in Hydrangea, temp of skin in siamese cats and Himalayan bunnies

Epistasis

• one gene expression can modify the expression of another

  • most traits are polygenic which means it takes more than one set of genes to create a particular characteristic

    • ex. heigh, hair color

  • the kind of gene that goes off influences how other genes are being used

  • dependency

Pleiotropy

• a single gene can exert a wide range of effects ex. sickle cell

• domino type affect

• causes numerous symptoms

• sickle cells leads to:

  • pain, circulation difficulties, heart failure, increase spleen size, increase risk of pneumonia

    • changing amino acid changes protein

Lethal Alleles

• may be recessive or dominant

• the homozygous condition results in the death of the organism

• ex. Genetic dwarf

  • has to be something that doesn’t kill the heterozygote like normal growth

  • interrupts major patternizations in this case cartilaginous growth

Expressivity

• the degree to which a trait is expressed in an individual ex. polydactyl limbs

  • not all symptoms may be expressed fully ex. extra toes on one foot but not the other

Pedigrees

• squares are males

• circles are females

• color symbols express traits

• white symbols do not

  • another type of probability and useful for tracing medical history

Alkaptonuria

• affect individual (purple) are unable to breakdown alkapton, which colors urine and stains tissues

Continous variation

• in most cases, the different expressions of traits in a given population is uniform (bell shaped curve distribution)

• ex. pigmentation, height, weight

Recessive

• expressed only in absence of dominant alleles

Gene Regulation in Eukaryotes

• control of this process is accomplished by binding of proteins to specific area of the DNA molecule (promotor regions) which serve as the initiator sites for RNA polymerase; these transcription factors can therefore influence gene activity

• there are other areas of the DNA (enhancer regions) which can affect the promotor

• degree of coiling of DNA influences availability of genes for transcription