Chapter 8: Chromosomes and Human Genetics (Bio 5)

Locus

-(plural "loci') -the physical location of a gene on a chromosome is called ---. -Because a gene can occur in different versions, or alleles, a diploid cell can have two different alleles at a given locus on pair of homologous for the gene. -Two alleles at a locus are different: -heterozygous -Two alleles at a locus are identical -homozygous

Dominant genetic disorder

-A more rare type of inherited disease is ---- caused by an autosomal dominant allele (A). -The allele that causes a disorder cannot hide in the same way that a recessive can: AA and Aa individuals get the disorders are more rare than recessive disorders because a ------ often produces serious negative effects immediately upon birth and individuals with A allele may not live long enough to reproduce.

Karayotype

-A scientist will take a photograph of a cell's chromosomes during mitosis and then pair up each set of homologous chromosomes to create a -----. - The autosomes are numbered 1 through 22 and sex chromosomes are designated X or Y.

Autosomes

-All the other chromosomes are called

Recessive Genetic Disorders (Single Gene)

-Both sexes are equally likely to be affected by both dominant and recessive genetic disorders on autosome -Both males and females have two copies of autosomal chromosomes -they have identiclal odds of being homozygous dominant, homozyhous recessive, or heterozygous for a disorder allele.

Females

-Human females have two copies of the X chromosomes -All the gametes (eggs) they produce contain one X chromosomes, passed on to their offspring.

Males

-Human males have one X chromosome and one Y chromosome - Half of their gametes (sperm) will contain an X chromosome. - Half will contain a Y chromosome.

Genetic Carriers

-Individual who have only one copy of a recessive allele are said to be ----- of the disorder -Carriers can pass on the disorder allele but they do not have the disease -To emphasize the fact that a trait is on the X chromosome: - A recessive X-linked allele a is denoted by Xa. - A dominant X-linked allele A is denoted by XA.

Sex Chromosomes

-Roughly 1240 of the estimated 20,000 human genes are found on the X & & Y Chromosomes -the X Chromosome carries 1,180 gene loci -But the Y Chromosome carries only 60

The SRY Gene

-Sex-determining Region of Y -The "master sex switch" -Determines that he growing embryo will be male -When present, SRY causes genes on some automates to produce male characteristics -When absent, autosomal genes produce female characteristics -Female is the default sex in humans -XY individuals whose SRY gene fails present with androgen insensitivity syndrome (AIS). -Though genetically male, they are physically female.

genetic engineering

-The permanent introduction of one or more genes into a cell, tissue or organism

Sex Linked

-There is 1240 genes which are called the ----.

pedigee

-a chart similar to a family tree that shows genetic relationships among family members over two or more generations of a family's medical history -Provides scientists with a way to analyze information to learn about the inheritance of a particular genetic trait or disorder

Genetic Disorder

-a disease excused by an inherited mutation passed down from a parent to a child n a gene, passed down from a parent to a child

Achondroplasia

-a form of dwarfism, is caused by a mutation in a gene involved in bone growth

gene threapy

-a technique for correcting defective genes responsible to disease envelopment -A type of genetic engineering

Chromosomal Abnormality

-any change in the chromosomes number or structure, compared to what is typical for a species. -Two most common types of chromosomal abnormalities in humans are: - Changes in the overall number of chromosomes (usually lethal) • Exceptions: sex chromosome number changes and - Changes in chromosome structure (have dramatic effects, such as a change in the length of an individual chromosome) • Example: cri du chat syndrome

Cystiv Fibrosis

-is is a recessive autosomal disease. -Zoe's parents were both carriers for cystic fibrosis, a recessive genetic disorder

Sex Chromosomes

-one of the the 23 pairs of human chromosomes consists -Determine whether a person is male or female. -Males have one X chromosome and one Y - Females have two X chromosomes

X-linked

-sex-linked genes on the X chromosome

Y-linked

-sex-linked genes on the Y chromosome -One of these Y-linked gened is the SRY Gene -SRY functions as the "masters sex switch" committing the sex of the developing embryo to male. In the absence of this gene, human embryo develops as females.

Huntington diease

-symptoms include uncontrolled movements and loss of intellectual faculties caused by dying brain cells

What is probability that a child with one parents who has autosomal dominant diorder will inherit the disease?

50%

What proportions of the male and female descendants in generation IV were affected by disorder?

50% (4/8 or 0.50) of males and 0% (0/4 or 0.00) of females

Draw a Punnet square with two Az parents What proportion of the offspring would you have disorder? What proportion would be normal?

75% of the offspring would have the disorder 25% would be normal.

How many male and how many female descendants (individuals that did not join the family by marriage) does generation IV of Aldrich's pedigree contain ?

8 males and 4 females.

In one sentence, explain how the terms "gene", "locus", and "chromosome" are related.

A gene is found at a particular location a locus on a chromosome

Create a Punnett square to illustrate the offspring that could result if Felix has children with non-carrier woman. What is the probability that a son would have WAS? What is the probability that a daughter would be carrier of WAS?

A son would have 0% probability of having WAS. A daughter would have a 100% probability of being a carrier.

What are the odds that a given egg cell will contain an X Chromosome? A y chromosome? what are those odds for a sperm cell?

An egg cell has a 100% chance of containing an X chromosomes and a 0% chance of containing a Y chromosome. for the sperm cell, the odds are 50/50 for both cases.

Create a mnemonic to help remember the four kinds of structural changes

Answers will vary

Why are there no carriers with a dominant gentic disorder?

Anyone with the gene would express the disorder.

Autosomal Recessive Allele

Autosomal recessive allele (a) disorder: - Affected individuals have two copies of that allele (aa). - Usually, when a child inherits a recessive genetic disorder, both parents are heterozygous. - They both have the genotype Aa.

If hair color were determined by single gene, what would be an example of the gene's alleles?

B for brown hair, b for blonde hair.

Sisters share the same X chromosome inherited from their father, but they may inherit different X chromosomes from their mother. What is the probability that brothers share the same Y chromosome? What is the probability that brothers share the same X chromosome?

Brothers have a 100% probability of sharing the same Y chromosome, and a 50% probability of sharing the same X chromosome.

The size of a chromosome correlates roughly with the number of genes residing on it. Why are an extra copy of chromosome 21 and a missing Y chromosomes two of the least damaging chromosomal abnormalities?

Chromosomes 21 and the Y chromosome are two of the smallest chromosomes so fewer genes would be affected by there being too many or too few of them compared to a larger chromosome

Which chromosomes contains the gene for cystic fibrosis? For Tay-Sachs disease? For sickle-cell diease?

Cystic Fibrosis: chromosome 7. Tay Sachs disease: Chromosome 15. Sickle cell disease chromosome 11

In your own words, explain why most single-gene disorders are recessive rather than dominant.

Dominant, single-gene disorders experience heavier selection than recessive disorders because they are always expresses there are no carries

In which part f meiosis would you predict that chromosomal abnormalities are produced?

During meta-phase, when paired chromosomes are separated.

Which of the children specified in this Punnett Square represents Felix? What is his genotype?

Felix is the affected son with genotype X^aY.

How do we know whether two chromosomes are homologous?

If the chromosomes carry alleles of the same genes and align during cell division, they are homologous.

Which two children in this pedigree have cystic fibrosis? How do you know?

Individual III-2 and III-3 have cystic fibrosis. They are depicted by filled symbols.

Is this the karyotypes of a male or a female?

Malle

Does either parent of these two children have cystic fibrosis? If so, which one(s)? How do you know?

Neither Parents II-1 nor II-2 has cystic fibrosis. They are both depicted by open symbols.

If a couple of two daughters, does that mean their next two children are more likely to be sons? Explain your reasoning.

No, the probability for each event is independent of prior and future events.

Explain why Felix is neither homozygous nor heterozygous for the WAS gene

The WAS gene is found on the X chromosome and Felix carried only one X chromosome because he is male. Only with two chromosomes are homozygous and heterozygous genotypes possible.

No know genetic disorder are encoded on the Y chromsome. Why do oyou think this is?

The Y chromosome has very few genes; further any disorder would always be expressed and therefore selected against

If Zoe is able to have child of her own someday and the other parents is not a carrier of cystic fibrosis ( he would likely be tested before they chose to have children,what is the probability that the child would have cystic fibrosis? that the child would be carrier?

The child would have 0% probability of having CF, and 100% probability of being a carrier.

If Zoe's parents had another child, what is the probability that the child would have cystic fibrosis? That the child would be CF carrier?

The child would have 25% (1/4) probability of having CF, and 50% (1/2) probability of being a carrier.

Why did Aldrich hypothesize that the disease was X-linked?

The disease was observed only in males but their mother's male relatives were also affected

How would he karyotype of a person of down syndrome differ from this karyotype?

There would be three copies of chromosome 21.

Does any of the grandparents of these two children have cystic fibrosis? If so, which one(s)? How do you know?

Yes, I-2, the paternal grandmother, has cystic fibrosis. She is depicted by a filled symbol

Which of the children in this Punnet Square represents Zoe? what is her genotype?

Zoe is the affected child with genotype aa.

Karyotype

a photograph of a cell's chromosomes during mitosis -Each set of homologous chromosomes is then paired up by hand

Chromosome Types

every species has a characteristic number of chromosomes. humans have 23 pairs of homologous chromosomes for a total of 46 Ex: Mosquitoes have only 3 pairs, or 6 in total.

Why are changes in chromosomes number almost always more severe than changes in chromosomes structure?

there are so many on an individual chromosomes that deleting or adding an entire chromosome has massive effects on an individual.