bio unit 7 (meiosis and genetics)

trait

the characteristics that an organism has, such as hair color, eye color, height, or skin color.

allele

Different versions of a gene that produce different traits in offspring.

Two alleles must be present in order for a trait to appear in the offspring. One allele is provided by each parent to the offspring.  When fertalization of sperm and egg occurs, the new offspring will have 2 alleles for each gene. 

gregor mendels laws

• The Law of Dominance and Recessiveness 

• The Principle of Segregation 

• The Principle of Independent Assortment

law of dominance and recessiveness

Some alleles are dominant, and others are recessive. A dominant allele can cover up or mask a recessive allele.

principal of segregation

Mendel’s Principle of Segregation says that every individual carries two alleles for each trait.

These two alleles separate or segregate during the formation of the egg and sperm cells.

the principle of independent assortment

when gametes are formed, the alleles of a gene for one trait segregate independently of the alleles of a gene for another trait.

phenotype

 physical characteristics of an organism or what the organism looks like

genotype

genetic makeup of an organism.

Probability

the likelihood that a particular event will occur.

Genes and the Environment

Gene expression is the result of the interaction of genetic potential with the environment. 

Incomplete Dominance or Nondominance

The phenotypes of the parents appear to blend or mix together in the phenotype of the offspring.

pink flowers

WW and RR

Codominance 

Both dominant alleles are apparent in the phenotype of the heterozygous offspring.

both alleles are fully expressed

blood

Multiple Alleles (polyallelic)

In genetics problems with multiple alleles, there are three or more alleles for the trait. (offspring still have two)

rabbits

Polygenic Inheritance

combined effect of many genes (eye color, hair, size, weight, height, etc)

A trait affected by a number of genes (polygenes) does not show a clear difference between groups of individuals.  

it shows a graduation of small differences. Many normal human traits are thought to be polygenic.

chromosomes gene linkage

Independent assortment cannot occur if Gene A and Gene B are linked together on the same chromosome.

A chromosome is a group of linked genes.  

During meiosis, it is the chromosomes that assort independently in gametes, not the individual genes.

AMAB / AFAB

assigned male/female at birth

female sex chromosomes

XX

male sex chromosomes

XY (y has less genes)

sex linked traits in humans include

olor blindness, hemophilia, and muscular dystrophy. These are caused by recessive alleles.

sex linked genes

Since assigned males at birth have only one copy of the X chromosome, they will have the disorder if they inherit just one copy of the allele.

Females assigned at birth must inherit two copies of the allele, one on each of their ___ chromo

Must the fathers of all colorblind girls be colorblind? Explain.

Yes. For a girl to be colorblind, she must inherit the colorblind allele from each parent.

mutations

A chromosome mutation involves either a change in the structure of a chromosome, or the gain or loss of an entire chromosome.

2. Chromosome mutations have a much more drastic effect on the organism than gene mutations because they involve the entire chromosome rather than just one gene.

3. Types of chromosome mutations include:  

Deletion, inversion, translocation, and nondisjunction.

Deletion

The loss of a piece of chromosome due to breakage.

Inversion

A segment of chromosome breaks off, flips around, and reattaches to the same chromosome.

Translocation

a piece of one chromosome breaks off and reattaches to a nonhomologous chromosome.

Nondisjunction

In nondisjunction the members of a pair of homologous chromosomes do not move apart properly during meiosis I, or sister chromatids fail to separate during meiosis II.

b) The result is that one gamete receives two of the same type of chromosome and another gamete receives no copy.  The other chromosomes are usually distributed normally.

If either of these gametes is then fertilized by a normal gamete, the zygote will have an abnormal chromosome number for that one particular chromosome.  

One zygote will have an extra chromosome, and the other zygote will be missing a chromosome.

down syndrome

smart

yes