exam 3 pt 2

Meiosis and sexual life cycles; each stage?

Sister chromatids

Half of a chromosome

• 23 pairs of chromosomes

• Each half is identical and have the same genes

Homologous Chromosomes

Same trait, different allele.

Allele

Different versions of a gene

(brown vs green eye color allele)

Non-Homologous Chromosomes

Chromosomes that carry different traits.

Locus

A gene’s location on a chromosome.

Haploid

Half of a set of chromosomes.

Diploid

One set of chromosomes.

Karyotype

Chromosomal makeup.

Human chromosome numbers

Humans contain 23 pairs of chromosomes (22 pairs of autosomes and 1 pair of sex chromosomes)

Sex Chromosomes

Chromosomes that determine the sex of an individual.

X chromosome is….

Known as the female chromosome

• X chromosome contains approximately 1,100 genes

Y chromosome is…

Known as the male chromosome

• Y chromosome contains approximately 450 genes

Genetics

Study of heredity.

Heredity

Transmission of traits from one generation to the next.

Trait

A variant of a character.

Character

A heritable feature that varies among individuals.

• hair color, eye color

Meiosis vs. Mitosis

• Mitosis produces diploid cells (one division, somatic cells)

• Meiosis produces haploid cells (two divisions, gametes)

Sperm & Oocyte anatomy

• Zona Pellucida egg membrane provides protection

• Only head of
  sperm penetrates membrane to form zygote.

haploid; in animals, plants, fungi

Sexual Reproducing Organism

• In animals only gametes are haploid.

• Plants and some algae have haploid multicellular stage.

• Fungi and some protist primarily have haploid unicellular stage.

Crossing Over

Exchange of genetic material between homologous chromosomes during meiosis (prophase 1)

Nondisjunction

Failure of chromosomes to separate properly during cell division.

Aneuploidy

When you have an abnormal number of chromosomes.

Trisomy 21

A condition caused when chromosome 21 fails to properly separate so there is an extra copy of chromosome 21.

• leading to Down Syndrome

  • Have two chromosomes at telophase 2+cytokinesis 2, creating 3 instead of 2

Trisomy 13

A condition associated with Patau Syndrome.

Turner Syndrome (X)

Condition where a female has only one X chromosome, resulting in being born with 45 chromosomes.

• Webbed neck, don’t go through traditional puberty

• Sterile

Klinefelter’s Syndrome (XXY)

Condition in males with two Xs and one Y

• have less body hair and breast enlargement

• Not sterile but tougher for reproduction

Jacob Syndrome (XYY)

Condition in males with an extra Y chromosome

• has more masculine features

• More testosterone

• Taller, excess acne, more lean / tougher to put on muscle

• Not much issue with reproduction

Egg meiosis

Egg completes meiosis and arrests (stops) in metaphase II after puberty.

1. Egg arrests ion prophase 1 after birth

2. After puberty egg completes meiosis and arrests in metaphase 2

3. After fertilization egg completes meiosis 2

Factors that create genetic variation

Besides mutations these three factors are required to maintain genetic variation within a population.

1. Crossing over

2. Independent Assortment

3. Random Fertilization

Random Fertilization

Creates different combinations of zygotes due to random fusion of gametes.

Genotype

Genetic makeup of an organism.

Phenotype

Physical makeup of the genotype.

Lamarck inheritance theory

acquired traits can be inherited

• Would say if their mother had the long neck phenotype then their kid will have the long neck characteristic but that is not the case since it is an acquired trait and you had to do something to acquire the long neck

• His theory was proven to be wrong

Mendelian inheritance theory

Conducted pea plant experiments to gather evidence to show how

traits are inherited.

• Determined dominant traits are expressed over recessive traits.

  • Additionally, determined organisms only inherit two copies of a gene.

• His hypothesis was that a trait is passed down from one generation to the next

  • Proved Lamarck theory as wrong

Homozygous dominant

An organism with two identical dominant alleles for a particular trait, such as AA.

Heterozygous

An organism with two different alleles for a particular trait, such as Aa.

Homozygous recessive

An organism with two identical recessive alleles for a particular trait, such as aa.

True breeding

Homozygous for specific alleles (homozygous dominant or recessive)

Complete Dominance

Dominant alleles mask the effect of recessive alleles.

Law of Segregation

Alleles are present for each trait and segregate during division

• Lowercase = recessive

• Uppercase = dominant

  • Happens during meiosis?

Law of Independent Assortment

Inheritance of one character gene does not affect the inheritance of another.

Recessive Disorders

Disorders that manifest if both alleles are recessive.

• Sickle cell

• Cystic Fibrosis

• Tay-Sachs

Common complete dominance condition where only the recessive phenotype expressed when both alleles are present.

Dominant Disorders

Disorders that manifest if at least one allele is dominant.

• Huntington’s disease

• Autosomal dominant polycystic kidney disease

• Osteopetrosis

Common complete dominance condition where the dominant phenotype is expressed even when only one dominant allele is present.

Incomplete Dominance

(partial dominance) (exception to Mendel’s rule)

Phenotype that is a mix of two different alleles.

• Carl Correns (1864-1933)

  • Snap dragon experiment

  • The intermediate phenotype of two traits

• Humans have a straight hair allele and curly hair allele. People who inherit both alleles have wavy hair.

Codominance

Both alleles in a heterozygote are fully expressed.

• Humans have three alleles for blood type A, B and O blood

• A and B are codominant, and O is recessive to both.

Epistasis

An interaction between genes where one gene influences the phenotype produced by another gene.

• Labrador example shown below Black is dominant to brown. However, pigment only deposited if pigment localization protein present. If it is not, the dog is yellow.

B= black

b= brown

E= pigment

e= no pigment

Exception:

• A allele —> directly affects B allele —> expression which then affects the phenotype

Polygenic Inheritance

Traits controlled by two or more genes.

(An exception to Mendel’s theory)

• such as skin color and height in humans.

• A and B allele both affect phenotype

Epigenetic Inheritance

Traits and DNA influenced by environmental factors over time

= sunlight / radiation , food & medicine you consume

• Challenges ideal genetic makeup is 100% a mixture of parent's DNA

• Variations in identical twins is a common example

Sex-linked traits

Traits associated with genes located on sex chromosomes.

• X chromosome is known as the female chromosome

• Y chromosome is known as the male chromosome

• X chromosome contains approximately 1,100 genes

• Y chromosome contains approximately 450 genes

Sex linked conditions

Men primary inherit sex linked traits

• Men lack extra X to mask recessive traits

Examples:

• Duchenne Muscular Dystrophy

• Hemophilia

• Color Blindness

Duchenne Muscular Dystrophy

Condition causing muscles to deteriorate because of a defective protein

• DMD gene is mutated over time that causes muscles to break down leading to heart failure and death around 15 years old

Hemophilia

Condition where the blood cannot form clots due to platelet defects = even a minor cut can cause bleed out and death

H= no hemophilia

h= hemophilia

XHY = make without hemophilia

XhY = male with hemophilia

XHXH = female without hemophilia

XHXh = female without but is a carrier