Science test

Heredity Review Vocabulary

  • Gene: Part of a chromosome/DNA that codes for a specific trait.

  • Allele: Different version or copy of a gene.

  • Homozygous (Purebred): Having two of the same allele (for example, BB or bb).

  • Heterozygous (Hybrid): Having two different alleles (for example, Bb).

  • Dominant: Allele that is always expressed over the other allele in the pair.

  • Recessive: Allele that is only expressed if both alleles in the pair are recessive.

  • Genotype: The genes an organism has (e.g., GG, Gg, gg).

  • Phenotype: The physical appearance or trait (e.g., blue eyes, long tail).

Types of Crosses

  • Monohybrid Cross: A cross done to track only one trait from parents to offspring.

  • Dihybrid Cross: A cross to track two traits from parents to offspring.

Patterns of Inheritance

  • Codominance: A pattern of inheritance in which an intermediate (hybrid) phenotype is shown when an individual has two different alleles (e.g., pink flower color with genotype Rr).

  • Incomplete Dominance: A pattern of inheritance where two different alleles paired together express both traits in a single phenotype (e.g., AB blood type, a cow with brown and white patches).

Karyotype and Pedigree

  • Karyotype: A complete set of an individual's chromosomes arranged in pairs to be studied.

  • Pedigree: A family tree showing marriage lines, offspring lines, and sibling lines allowing for the tracing of a specific trait.

Gregor Mendel's Contributions

  • Mendel's Objective: Mendel was looking to discover how different traits can be passed from parent to offspring.

  • Parental Generation (P): Mendel crossed a plant with dominant traits to a plant with recessive traits.

  • F1 Generation Offspring: The offspring of the F1 generation all looked exactly the same as the dominant parent plant.

  • Segregation of Alleles: Recessive traits were not observed again until the F2 generation due to the segregation of alleles during gamete formation.

Genotypes and Phenotypes Examples

  • How to represent an allele for a dominant trait: A capital letter.

  • How to represent an allele for a recessive trait: A lowercase letter.

  • Examples:

    • BB, Bb, bb are examples of a Genotype.

    • Brown fur is an example of a Phenotype.

  • Highlight Answers:

    • BB is homozygous.

    • Yy is heterozygous.

    • Gg is heterozygous.

Traits Example in Animals

  • Curly tails are dominant to straight tails in pigs represented by the letters T or t.

  • Genotypes of a Pig with Curly Tail: TT or Tt.

Punnett Squares

  • A pig heterozygous (Tt) for a curly tail mates with a pig that has a straight tail (tt).

T

t

T

Tt

t

Tt

  • Results:

    • Total offspring with Brown fur: 4.

    • Total homozygotes: 2.

    • Total heterozygotes: 2.

Dihybrid Crosses

  • Number of traits that can be tracked with a dihybrid cross: 2.

FOIL Method in Genetic Crosses

  • FOIL Method: Stands for First, Outside, Inside, Last. Used to determine the possible gametes (combinations of alleles) each parent can produce.

  • Parents with genotypes:

    • Parent 1: BBGG

    • Parent 2: BbGg

  • Gametes generated:

    • For BBGG: BG, BG, BG, BG.

    • For BbGg: BG, Bg, bG, bg.

Dihybrid Cross Example with Traits

  • Traits: W is dominant to w, and Y is dominant to y.

  • Parents with genotypes WWYY and Wwyy are crossed.


WY

WY

WY

WY

Wy

WWYy

WWYy

WWYy

WWYy

wy

WwYy

WwYy

WwYy

WwYy

  • Possible Genotypes of Offspring:

    • WWYy, WwYy.

Example Plant Crosses and Offspring Phenotypes

  • Dominant traits example: R (red petals) is dominant to r (white petals) and S (long stem) is dominant to s (short stem).

  • Plant heterozygous for red petals and long stems is crossed with another plant heterozygous for red petals and long stems (RrSs x RrSs).

  • Gametes produced: RS, Rs, rS, rs from each parent.


RS

Rs

rS

rs

RS

RRSS

RRSs

RrSS

RrSs

Rs

RRSs

RRss

RrSs

Rrss

rS

RrSS

RrSs

rrSS

rrSs

rs

RrSs

Rrss

rrSs

rrss

  • Phenotype Ratios of Offspring:

    • Red Tall: 9.

    • Red Short: 3.

    • White Tall: 3.

    • White Short: 1.

Incomplete Dominance and Codominance

  • Incomplete Dominance: Inheritance pattern that creates intermediate or hybrid phenotypes.

  • Example: R (red petals) is dominant to r (white petals).

  • Genotype Representation:

    • Red Flower: RR.

    • White Flower: rr.

    • Pink Flower: Rr.

Simplified Cat Tail Length Example

  • Tail length in cats is determined by alleles H and h.

  • H (long tails) is dominant to h (short tails). Medium length tails are an intermediate expression.

  • Genotypes and Phenotypes of Offspring:

    • Cross: HH (Long tail) x Hh (Medium tail).

    • Results:

    • Offspring: HH (Long tail), Hh (Medium tail).

Codominance in Blood Types

  • In blood types, codominance results in a phenotype from the combination of alleles.

  • Blood Types: A blood types, B blood types, AB blood types, and O blood types.

  • Phenotype Creation: AB blood type represents the combination where both alleles create a new phenotype.

Karyotype Importance

  • What is a Karyotype?: A complete set of an individual's chromosomes arranged into pairs for study.

  • Purpose: Used to look for chromosome abnormalities.

  • Sex Determination: Yes, a Y chromosome indicates male, whereas absence indicates female.

Pedigree Analysis

  • Utility of Pedigrees: Track a trait through generations of offspring.

  • Symbols Used: Squares represent males, circles represent females.

  • Recessive Phenotype Representation: Individuals shaded in a pedigree indicate recessive phenotypes.

    • Example Individuals: I2, II3, II5, III3, III4, III5.

  • Genotype of Individual II6: Heterozygous Bb, having one recessive allele from a shaded female and one dominant allele from a non-shaded male.

  • Genotypes of III1 and III2: They are both either homozygous or heterozygous, represented as BB or bb.