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Human HeredityChapter 14

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Human Chromosomes

To understand what a human is, biologists have beganstudying inside the human cell, to the chromosomes.

Biologists examine cells at the time of mitosis.

Cutting out the chromosomes from photographs and grouping

them together. Making what is known as a Karyotype

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Terms and Definitions

Chromosome - is an organized package of DNAfound in the nucleus of the cell.

Humans have 23 pairs of chromosomes--22 pairs

of numbered chromosomes, called autosomes, and

one pair of sex chromosomes, X and Y. Each parent contributes one chromosome to each

pair so that offspring get half of their chromosomes

from their mother and half from their father.

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Haploid- Haploid is the quality of a cell or organismhaving a single set of chromosomes. Organisms

that reproduce asexually are haploid.

Sexually reproducing organisms are diploid (having

two sets of chromosomes, one from each parent).In humans, only their egg and sperm cells are

haploid.

Diploid- is a cell or organism that has paired

chromosomes, one from each parent. In humans,cells other than human sex cells, are diploid and

have 23 pairs of chromosomes.

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Sex Chromosomes- A sex chromosome is a type ofchromosome that participates in sex determination.

Humans and most other mammals have two sex

chromosomes, the X and the Y. Females have two

X chromosomes in their cells, while males haveboth X and a Y chromosomes.

Egg cells all contain an X chromosome, while

sperm cells contain an X or Y chromosome. This

arrangement means that it is the male thatdetermines the sex of the offspring when

fertilization occurs.

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Autosomes- An autosome is any of the numberedchromosomes, as opposed to the sex chromosomes.

Autosomes are numbered roughly in relation to their sizes.

That is, Chromosome 1 has approximately 2,800 genes,

while chromosome 22 has approximately 750 genes.

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Human Traits

Human genes are inherited.

Using the same principles as set out by Gregor

Mendel and his peas.

Using a pedigree chart we can show relationships

within a family.

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80 generation pedigree chart

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Human Genes

Blood Groups- blood groups come in avariety of types.

Blood groups

AB+ O+

B+ A+

A- O-

B- AB-

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Rh Blood Group

Rh blood group is determined by asingle gene with two alleles positive

and negative.

The positive (Rh+) allele is dominant.So a person with Rh+/Rh+ or Rh+/Rh-

are said to be Rh-positive.

Those with two Rh- alleles are Rh-negative.

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ABO blood group

There are three alleles for this gene I a, Ib, andi .

I a and I b are codominant and they producemolecule know as antigens on the surface of

red blood cells Individuals with alleles I a and I b produce the

blood type AB.

The i is recessive.

People with Ia Ia or Iai produce only A antigens People with Ib Ib or Ibi produce only B

antigens.

Those with ii allele produce no antigen and

have the blood type O.

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Recessive Alleles

Human genes have become knownthrough the study of genetic disorders.

Cystic Fibrosis

Sickle Cell Anemia

Tay Sachs Disease

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From Gene to Molecule

What is the link between the DNAbases in the allele for genetic disorder

and the disorder itself?

In both cystic fibrosis and sickle celldisease, a small change in the DNA of

a single gene affects the structure of a

protein, causing a serious geneticdisorder.

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Cystic Fibrosis

CF, is common among peoplewhose ancestors came from

Northern Europe.

The disease is caused by arecessive allele on chromosome 7.

Children with CF ha serious

digestive problems, and produce a

thick heavy mucus that clogs thelungs

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Sickle Cell Disease

Common genetic disorder found in African Americans.

Red blood cells are bent and

twisted shape of a sickle and tendto get stuck in the capillaries.

Result: blood stops moving

through the vessels, damaging

cells, tissues and organs.

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SCD Cont…

Why do so many African Americans carrythe SC allele?

Most African Americans can trace their

ancestry to West Central Africa. Malaria, aparasitic disease infects red blood cells is

common in that area.

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Huntington’s Disease

Huntington's Disease (HD) is a braindisorder that affects a person's ability tothink, talk, and move.

The disease destroys cells in the basal

ganglia, the part of the brain that controlsmovement, emotion, and cognitive ability.HD is caused by a mutation in a gene onchromosome.

Huntington's disease is inherited in anautosomal dominant pattern. This meansthat everyone who inherits the faulty genewill eventually get the disease.

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X Chromosome

The X chromosome carries nearly 1,000genes but few, if any, of these have

anything to do directly with sex. However,

the inheritance of these genes follows

special rules. These arise because:

•males have only a single X chromosome

•almost all the genes on the X have no

counterpart on the Y. •Any gene on the X, even if recessive in

females, will be expressed in males.

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X-Linked

Genes inherited as previouslymentioned are described as sex-linked

or, more precisely, X-linked.

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Hemophilia

Hemophilia is a blood clotting disordercaused by a mutant gene encoding

either,

1) clotting factor VIII, causing hemophilia A

2) clotting factor IX, causing hemophilia B

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Heterozygous females are

called "carriers" because

although they show nosymptoms, they pass the

gene on to approximately

half their sons, who

develop the disease, andhalf their daughters, who

also become carriers.

Queen Victoria

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Y Chromosome

Each person normally has one pair of sexchromosomes in each cell. The Ychromosome is present in males, who haveone X and one Y chromosome, while females

have two X chromosomes. Many genes are unique to the Y

chromosome, but genes in areas known aspseudoautosomal regions are present on

both sex chromosomes. As a result, men andwomen each have two functional copies ofthese genes. Many genes in thepseudoautosomal regions are essential fornormal development.

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Y Genetic Disorder

Many genetic conditions are related tochanges in particular genes on the Y

chromosome.

A. Langer mesomelic dysplasiaB. Léri-Weill dyschondrosteosis

C. Swyer syndrome

D. 46,XX testicular disorder of sex

development

E. Y chromosome infertility

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Chromosomal Disorders

These are common errors in meiosis.The most common occurs when

homologous chromosomes fail to

separate. This is callednondisjunction.

If nondisjunction occurs, abnormal

numbers of chromosomes may findtheir way into gametes, and a disorder

of chromosome numbers may result.

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Down Syndrome

Down's syndrome, also known as

trisomy 21, is a genetic disorder

caused by the presence of all or partof a third copy of chromosome 21.

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It is typically associated with physicalgrowth delays, characteristic facial

features and mild to moderate

intellectual disability.. The average IQ of a young adult with

Down syndrome is 50, similar to the

mental age of an 8 or 9 year old child,but this varies widely.

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