Anatomy & Physiology I Unit Five

The Characteristics and Functions of Meiosis Production of gametes Assures correct chromosome numbers in offspring Creates new combinations of genes Begins with a diploid sex cell & ends with non-identical haploid gametes

Meiosis Meiosis is the cell division process by which gametes are produced It occurs only in sex cells that are found in the gonads

Meiosis The process goes through two meiotic divisions – meiosis I and meiosis II

Meiosis Homologous chromosomes

Meiosis

Meiosis

Meiosis

Meiosis vs. Mitosis

Genetics Genetics – the study of heredity Heredity – the passing of traits from one generation to the next Trait – a physical or physiological characteristic coded for by a gene Gene – a portion of a chromosome that codes for a particular protein Allele – a form of a gene

Genetics Dominant allele – an allele that masks the effects of the other Recessive allele – an allele that can be masked by a dominant allele Locus – the position of a gene on a chromosome

Genetics Homologous chromosomes – a pair of chromosomes, one each from the female & male parent, that have identical structure and gene loci

Homologous chromosomes Genetics Mom (female) Dad (male) Recessive allele Dominant allele Homologous chromosomes

Genetics Genotype – the set of genes an organism has Homozygous – alleles are the same type Heterozygous – alleles are different

Genetics Phenotype – the expression of the genotype Purebred – having a homozygous genotype Hybrid – having a heterozygous genotype

Genetics Codominance – the two alleles at a locus are equally expressed Karyotype – a chart of the chromosomes of an organism, arranged in order by size and structure

Genetics

D D d d D d

D D Dd d Punnett Square

D D d d D d D d D D d d

D d DD Dd dd D d Complete Dominance Monohybrid Cross Genotypic Ratio – 1:2:1 Phenotypic Ratio – 3:1

Complete Dominance

D d Dd dd d Complete Dominance Monohybrid Cross Genotypic Ratio – 2:2 Phenotypic Ratio – 2:2

A O AB BO AO OO B O Codominance Genotypic Ratio – 1:1:1:1 Phenotypic Ratio – 1:1:1:1

Autosomal vs. Sex Linked Autosomes – all chromosomes except for the ones that determine sex Sex chromosomes – chromosomes that determine sex Sex linked traits – traits controlled by genes on the sex chromosomes

XB Xb XBXb XbXb XBY XbY Xb Y Sex Linked Cross

Human Sex Chromosomes ♀ ♂ X X X Y

Human Sex Chromosomes ♀ ♂

Mutations A mutation is any change in the DNA of an organism Mutations occur due to: - pathogen infection - exposure to radiation - introduction of chemicals - nondisjunction

Mutations Mutations involve: - base pair substitutions - base pair insertions or deletions - DNA segments

Mutations

Genes, Genetic Code & Genetic Disease Remember, genes are portions of DNA that code for a particular protein In order for the protein to be functional, the DNA nitrogen base sequence must be correct

Genes, Genetic Code & Genetic Disease Any variance of that sequence can cause the wrong amino acid to be inserted into the polypeptide which could result in: - a non-functioning protein - a protein that changes the outcome of a process

Nondisjunction Nondisjunction is the failure of chromosomes to separate during anaphase I of meiosis The normal separation, disjunction, produces daughter cells with 23 chromosomes each

Nondisjunction Nondisjunction results in one daughter cell with 24 chromosomes and the other with 22 chromosomes

Nondisjunction Monosomy is the result of the fertilization of a normal gamete and one that has only 22 chromosomes Trisomy is the product of the fertilization of a normal gamete and one that has 24 chromosomes

Disjunction Nondisjunction

Genetic Disorders Several genetic disorders are sex linked and found predominantly in men, but can also be present in women The shorter Y chromosome means there is only one allele that determines these traits

Genetic Disorders Male pattern baldness and color blindness are two examples that are inconvenient, but non-life threatening Hemophilia, a condition in which the blood does not clot correctly, can be deadly

Genetic Disorders Remember: Any variance of the DNA base sequence can cause the wrong amino acid to be inserted into the polypeptide which could result in: - a non-functioning protein - a protein that changes the outcome of a process

Genetic Disorders These mutations can lead to a number of human health disorders Some of these abnormalities are inconvenient, while others can be lethal

Genetic Disorders Albinism is a condition in which the body does not produce the pigment melanin The phenotypic results are white hair, pale skin and pink colored eyes

Genetic Disorders Albinism is the result of a homozygous recessive genotype that produces a nonfunctional tyrosinase enzyme Melanin is synthesized from tyrosine by way of the enzyme tyrosinase

Genetic Disorders Sickle cell disease is a condition in which red blood cells are deformed due to the substitution of one amino acid in a hemoglobin chain

Genetic Disorders The deformation of the RBCs inhibits the binding of oxygen, causing anemia The deformation also causes the sickled RBCs to be sticky and agglutinate

Genetic Disorders Without treatment a child will usually die before age two Even with treatment most affected people die before the age of fifty

Genetic Disorders The substitution of one amino acid is caused by a recessive allele Sickle cell is the result of a homozygous recessive genotype that produces the malformed hemoglobin

Genetic Disorders Approximately 8.5% of people of central and southern African descent are carriers of the allele

Genetic Disorders Phenylketonuria (PKU disease) is a disorder in which the amino acid phenylalanine is not metabolized due to the lack of an enzyme

Genetic Disorders PKU disease is the result of a homozygous recessive genotype that does not produce the enzyme that converts phenylalanine into tyrosine

Genetic Disorders Phenylalanine accumulates in the blood and acts as a neurotoxin, causing brain damage and retardation Required tests on newborns now identify those affected, which will be put on a low phenylalanine diet

Genetic Disorders Remember: Nondisjunction in gametes causes a change in chromosome numbers that affects the development of an embryo Approximately 90% of nondisjunction events are maternal in origin

Genetic Disorders The presence of an extra chromosome (trisomy) or lack of one (monosomy) accounts for approximately 50% of all spontaneous abortions

Genetic Disorders Only three autosomal trisomies are survivable: * trisomy 13 – Patau syndrome * trisomy 18 – Edward syndrome * trisomy 21 – Down syndrome

Genetic Disorders Most fetuses with Patau or Edward syndrome will die before birth The few that are born are severely deformed and usually die within their first year

Genetic Disorders Karyotype of Down syndrome (trisomy 21)

Genetic Disorders Down syndrome is the most survivable of the trisomies, but approximately 75% die before birth and 20% of those born will die before the age of ten

Genetic Disorders Down syndrome effects: * short stature * a flat face with almond shaped eyes * enlarged protruding tongue * broad hands with short fingers * varying degrees of mental retardation

Genetic Disorders Of those that survive past the age of ten, life expectancy has been extended to sixty years However, after the age of forty many develop early onset Alzheimer disease

Genetic Disorders Nondisjunction also occurs with the sex chromosomes: * trisomy 23 – Klinefelter syndrome (XXY) * trisomy 23 – Triplo-X syndrome (XXX) * monosomy 23 – Turner syndrome (XO)

Genetic Disorders Triplo-X syndrome (XXX) results in a female phenotype that is usually infertile and may exhibit some intellectual impairment

Genetic Disorders Klinefelter syndrome (XXY) results in a sterile male phenotype that is of normal intelligence and upon the onset of puberty exhibits unusually long arms, sparse body hair, undeveloped testes and enlarged breasts

Genetic Disorders Turner syndrome (XO) results in a sterile female phenotype that fails to develop secondary sex characteristics at puberty and is usually short in stature Approximately 97% of all (XO) fetuses die before birth