exam 3 pt 2

Meiosis and sexual life cycles

Key terms:

·      Sister chromatids: Half of a chromosome.

o   23 pairs of chromosomes

o   Each half is identical and have the same genes

·      Homologous Chromosomes: Same trait different allele.

o   Allele = different versions of a gene

·      Non-Homologous Chromosomes: 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 Chromosomes

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

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

·      Which chromosome is better for survival?

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.

o   Eye color, hair color

·      Genetics: Study of heredity.

·      Karyotype: Chromosomal make-up.

Meiosis vs Mitosis

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

·      Meiosis produces haploid cells (two divisions, gametes)

Sperm and Oocyte Anatomy

·      Zona Pellucida egg membrane provides protection. Only head of
sperm penetrates membrane to form zygote.

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.

Mitosis vs Meiosis: meoba sisters video

Prophase I

·      Mitotic spindle forms, chromosomes condense, and nuclear envelope
disappears.

·      Crossing over occurs at chiasmata.

o   Chiasmata is the location where non sister chromatids intersect.

·      Microtubules (centrosome) attach to kinetochores at the centromere.

Metaphase I

·      Chromosomes line up on metaphase plate. Chromatids of one
homologous pair is attached to microtubules on one pole, chromatids
of other homolog is attached to microtubules at opposite pole.

Anaphase I

·      Proteins that hold homologous chromosomes together are degraded
and homologous chromosomes are pulled to opposite poles.

Telophase I & Cytokinesis I

·      Telophase I- Nucleus divides, nuclear envelop reappears, spindles
disappear

·      Cytokinesis I- Cytoplasm divides

Prophase II

·      Mitotic spindle forms, chromosomes condense, and nuclear envelope
disappears.

·      Microtubules (centrosome) attach to kinetochores at the centromere

·      No crossing over occurs at this point.

Metaphase II

·      Chromosomes line up on metaphase plate. Remember due to
crossing over sister chromatids are not identical.

Anaphase II

·      Breakdown of proteins that hold sister chromatids together.

·      Sister chromatids separate and are pulled to opposite poles.

Telophase II & Cytokinesis II

·      Nuclear envelope reappears, chromosomes become less condense
and microtubules disassemble.

Nondisjunction (Causes Aneuploidy)

·      Chromosomes fail too properly separate.

o   Aneuploidy: Abnormal number of chromosomes

·      Trisomy 21- Chromosome 21 fails to properly separate leads to Down Syndrome.

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

·      Trisomy 13- Patau Syndrome

Nondisjunction of Sex Chromosomes

Turner Syndrome (X)

·      Female only receives 1 X born with 45 chromosomes

·      Webbed neck, don’t go through traditional puberty

·      Sterile

Klinefelter’s Syndrome (XXY)

·      Less body hair

·      Not sterile but tougher for reproduction

Jacob Syndrome (XYY)

·      More masculine features

·      More testosterone

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

·      Not much issue with reproduction

Egg meiosis

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

(arrest = stops)

Factors that Create Genetic Variation

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

o   Crossing over: Creates recombinant chromosomes. (happens during prophase 1)

o   Independent Assortment: Creates different combinations of genetic material in gametes.

o   Random Fertilization: Creates different combinations of zygotes.

Crossing Over and Synapsis

(Mainly just need to know that crossing over is the exchange between homologus chromosomes and exchange genetic material, happens?)

1.     Homologous chromosomes align precisely (corresponding genes match up) DNA of non-sister chromatids is broken by specific proteins.

2.     Synaptonemal complex holds homologous chromosomes (sister chromatids) tightly together,
chromosomes now in synapsis.

3.     Broken ends are fixed by joining segment of sister chromatid from homologous chromosome.

4.     Synaptonemal complex dissembles and chromatids. Begin moving towards metaphase plate

Independent Assortment

·      Chromosomes (and by extension alleles) are sorted into gametes
independently of other genes.

Random Fertilization

·      How many different chromosome combinations can you have through random
fertilization?

·      Significantly more than trillions !

·      If you had the opportunity, would you determine the genetic make-up of your
offspring?

Mendel and the gene idea

Key terminology

·      Genotype: genetic makeup

·      Phenotype: physical makeup

·      Allele: different versions of gene (brown vs green eye color allele)

·      Heredity: transmission of traits from one generation to the next

·      Trait: a variant of a character

·      Character: A heritable feature that varies among individuals

·      Genetics: Study of heredity

Lamarck inheritance

·      Jean Baptize Lamarck (1744-1829)

·      Lamarck inheritance: acquired traits can be inherited

o   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

o   His theory was proven to be wrong

Mendelian Inheritance

·      Gregor Mendel (1822-1884)

·      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.

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

o   Proved Lamarck theory as wrong

·      Key terminology:

Þ   Homozygous dominant

Þ   Heterozygous

Þ   Homozygous recessive

o   True-Breeding: Homozygous for specific alleles (homozygous dominant or recessive)

Þ   P generation (parental generation)

Þ   F1 generation (parental generation offspring)

Þ   F2 generation( F1 generation offspring)

o   Dominant traits mass recessive traits

o   Everyone has two copies of these genes; one from mom and one from dad

§  Determine these from punnent square

Example:

B= brown eyes

b= blue eyes

BB = homozygous dominant

Bb= heterozygous

bb= homozygous recessive

Differences in Alleles Example

Law of Segregation

·      Alleles are present for each trait and segregate during division

o   Lowercase = recessive

o   Uppercase = dominant

·      Happens during meiosis?

Law of independent assortment

·      The inheritance of one character has no impact on the inheritance of another character

Common Complete Dominance Conditions

Recessive Disorders

·      Sickle cell

·      Cystic Fibrosis

·      Tay-Sachs

Dominant Disorders

·      Huntington’s disease

·      Autosomal dominant polycystic kidney disease

·      Osteopetrosis

Exceptions to Mendelian Inheritance

·      Mendel stated that dominant alleles mask recessive alleles for a given trait.

There are several exceptions to this rule;

-       Incomplete dominance

-       Codominance

-       Epistasis

-       Polygenic Inheritance

-        Epigenetic Inheritance

Incomplete dominance (Partial Dominance)

·      Carl Correns (1864-1933)

·      Snap dragon experiment

·      The intermediate phenotype of two traits

Incomplete Dominance in Humans

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

Codominance

·      Two traits are equally dominant therefore both are present

·      Calico cat is an example in which multiple colors are being expressed.

Codominance in humans

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

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

Epistasis

·      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.

Polygenic Inheritance

·      Traits are controlled by two or more genes

·      Skin color

Epigenetic Inheritance

·      Traits are influence by environment

·      Challenges ideal genetic make-up is 100% a mixture of parent's DNA

·      Variations in identical twins is a common example

Sex linked traits

·      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 Liked 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

·      Muscles deteriorate as result of degradation of essential muscle proteins.

Hemophilia

·      Blood unable to form clots, due to defects in platelets

Determining Probability

·      Multiplication rule: Multiply probability of two independent events occurring at the same time (or from same sample group at different times)

·      Addition rule: Add probability of two mutually exclusive events.