Heredity (LE)

Genes

- segments of DNA that carry hereditary instructions (coded instructions for making proteins); - copies are passed from parent to offspring; - located on chromosomes

State Mendel's conclusions:

1. Each trait is controlled by a pair of "factors" (***Factors later became known as genes. Mendel had NO knowledge of DNA and genes.**) 2. An individual inherits TWO copies of a gene (one from each parent) 3. The two inherited factors could be alike (ex: TT or tt) or different (Tt) 4. When different alleles occur together, one may be completely expressed while the other is hidden. (Law of Dominance) 5. The two factors separate during gamete formation and recombine during fertilization. (Law of Segregation)

Give examples of how traits can be influenced by the environment

1. Hydrangea flowers with the same genotype will have different flower colors depending on the acidity of the soil. Acidic soil results in blue flowers while flowers are pink in neutral to basic soils 2. Human height is influenced by nutrition as well as genes 3. The fur color of the artic fox is affected by temperature. Pigment producing genes are turned OFF in the winter resulting in white fur (which is better for blending into the snowy environment); Pigment producing genes are turned ON in the summer resulting in reddish brown fur

When two hybrid tall pea plants are crossed, the GENOTYPE ratio is observed in the offspring?

1: 2: 1 TT: Tt: tt

How many chromosomes are in human sex cells (egg cells and sperm cells)?

23 sex cells are haploid - they contain only 1 set of chromosomes; Only ONE chromosomes from a homologous pair

When two hybrid black guinea pigs are crossed, the probability of a white guinea pig is: (Note: Black coat color is dominant to white coat color)

25% white

When two hybrid tall pea plants are crossed, the PHENOTYPE ratio is observed in the offspring?

3:1 Dominant: recessive Tall : short

How many chromosomes are in human body cells?

46 (23 pairs) body cells are diploid - they contain 2 sets of chromosomes or homologous pairs

State the genotypes of the offspring for the following cross: Pp x pp **Do a Punnett Square to figure it out**

50% hybrid (Pp) 50% pure recessive (pp)

State the phenotypes for the following cross: Pp x pp

50% purple flower 50% white flower

When two hybrid black guinea pigs are crossed, the probability of a black guinea pig is: (Note: Black coat color is dominant to white coat color)

75% black

DRAW a punnett square (on paper) showing the cross between two heterozygous Gg parents. DETERMINE the percentage of green (G) offspring and yellow (g) offspring.

75% green offspring & 25% yellow offspring

Purple flower (P) is dominant over white flower (p) in pea plants. If two pea plants that are both hybrid for flower color are crossed, what will the offspring plants look like? **Set up a Punnett square to figure it out**

75% purple flower 25% white flower

Pedigree

A chart or "family tree" that tracks which members of a family have a particular trait

Codominance

A condition in which both alleles for a gene are fully expressed at the same time without "blending" together

monohybrid cross

A cross between hybrid individuals involving only one trait. Ex: Tt x Tt

If B - represents the allele for brown eyes and b represents the allele for blue eye, then an individual with the genotype Bb will have the phenotype of ______ eyes.

Bb (genotype) creates brown eye phenotype

If ALL offspring of a cross have the genotype Aa, the parents of the crosses would most likely be (choose one below) 1 - AA x AA 2 - AA x aa 3 - aa x aa 4 - Aa x Aa

Choice (2) AA x aa

If HALF the offspring of a cross have the genotype Aa and HALF are aa, the parents of the crosses would most likely be (choose one below) 1 - AA x AA 2 - AA x aa 3 - aa x aa 4 - Aa x aa

Choice (4) - Aa x aa

What is the molecule of heredity in all living things like plants and animals?

DNA

Who is the father of heredity?

Gregor Mendel used pea plants to study the way traits are passed from parent to offspring. **He performed each pea plant cross MANY times, counted the number of each kind of offspring and analyze the results. His mathematical analysis of data led him to observe patterns and predictable ratios when certain crosses were performed. ***Mendel LACKED knowledge of DNA and chromosomes, yet formulated 3 laws of heredity (Dominance, Segregation and Independent Assortment).

Law of Segregation

Mendel's law that states that the pairs of homologous chromosomes separate in meiosis so that only one chromosome from each pair is present in each gamete

incomplete dominance

Neither allele is completely dominant or recessive. BOTH alleles influence the phenotype of the trait. A hybrid individual has an INTERMEDIATE phenotype. Ex: RR = red, WW = white, *RW = pink (pink is intermediate between red and white)

Why were pea plants a good choice for Mendel's experiments?

Pea plants: 1. have traits that exist in ONLY TWO clearly different forms. 2. are capable of cross-pollination and self-pollination 3. grow easily, mature quickly and produce many offpsring

Identify the pedigree symbols for: a male, a female, an affect individual and a carrier.

Squares are male. Circles are females. Shaded means you have disease (or trait in question). Half shaded means you are a carrier

How are genotype and phenotype related?

The phenotype (appearance) depends on the genotype (the inherited combination of alleles)

sex-linked traits

Traits controlled by genes located on the sex chromosome (X). Ex: Hemophilia color blindness **Males are NEVER carrier of a sex-linked trait since they only have one X chromosome. --> Mothers can pass the allele to their sons (since the mother gives the X chromosome and the father gives the Y chromosome. --> Females can be unaffected, CARRIERS or affected (if they have two copies of the recessive allele)

Punnett Square

a tool used to predict the genotypes and phenotypes of offspring when both parents alleles are known. - gives expected results (not necessarily the actual results). ** Actual results match the expected (predicted) ratios of the Punnett square when there are LARGE numbers of offspring. -in a four box chart, each box is worth 25%

test cross

breeding that can be used to determine the genotype of an organism with the dominant phenotype. The phenotypically dominant organism is crossed with an organism that is pure recessive for the trait. Ex: T_?_ x tt IF any of the offspring show the recessive phenotype, then the parent in question is HYBRID. If none of the offspring show the recessive phenotype, then the parent in questions is assumed to be HOMOZYGOUS. NOTE: Large numbers of offspring should be used.

Law of Dominance and Recessiveness

certain alleles (dominant) can mask or hide the effect of other alleles (recessive) when they occur in pairs. Dominant alleles will be expressed when only ONE is present in a gene pair, while recessive alleles are expressed only when they occur in PAIRS..

Bears have a gene that codes for black or brown fur. The allele for black fur (B) is dominant over the allele for brown fur (b). Which combination of parental genotypes could produce offspring with black fur as well as offspring with brown fur? Choose one below. A - BB x BB B - Bb x Bb C - BB x bb D - bb x bb

choice (B) - Bb x Bb

Alleles

different forms of a single gene; represented by letters

a synonym for heterozygous

hybrid

polygenic inheritance

occurs when multiple genes determine the phenotype of a single trait EX: Polygenic traits include: skin color, eye color, height, weight, hair color (typically these are traits with a very WIDE range of possible phenotypes)

a synonym for homozygous

pure

Dominant allele

represented by a capital letter -the allele that is expressed in a hybrid when only one copy of the allele is inherited

Recessive allele

represented by a lowercase letter - the allele that is NOT expressed in a hybrid— it remains "hidden" -TWO copies of the allele must be inherited in order to be expressed

Phenotype

the appearance of an organism (The phenotype depends on the organism's genotype.)

Genotype

the inherited combination of alleles Ex: aa, Ee, FF, tt - described by using the terms pure/homozygous and hybrid/heterozygous

Homozygous

the scientific term for a genotype with 2 identical alleles; may be two dominant or two recessive alleles. Ex: AA or aa synonym: pure

Heterozygous

the scientific term for a genotype with one dominant allele and one recessive allele. Ex: Aa (two DIFFERENT alleles) synonym: hybrid

Genetics

the study of heredity

Heredity

the study of the passing of genetic information (traits) from one generation to the next (parent to offspring).

Multiple alleles

three or more forms of a gene that code for a single trait Ex: Human blood type— an individual inherits 2 of 3 possible alleles